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Collembola switch diet in presence of plant roots thereby functioning as herbivores
Abstract
Collembola are abundant and ubiquitous soil decomposers, being particularly active in the rhizosphere of plants where they are assumed to be attracted by high microbial activity and biomass. While feeding on root associated microorganisms or organic matter they may also ingest plant roots, e.g. particularly root hairs and fine roots. Employing stable isotope analysis we investigated Collembola (Protaphorura fimata Gisin) feeding preferences and types of ingested resources. We offered Collembola two resources with distinct isotope signatures: a C4 plant (Zea mays L.) planted in soil mixed with 15N labelled litter of Lolium perenne L. (C3 plant). We hypothesised that Collembola obtain their nutrients (C and N) from different resources, with their carbon being mainly derived from resources that are closely associated to the plant root, e.g. root exudates, causing enrichment in 13C in Collembola tissue, while the incorporated nitrogen originating from litter resources. In contrast to our hypothesis, stable isotope analysis suggests that in absence of plant roots Collembola derived both the incorporated C and N predominantly from litter whereas in presence of plant roots they switched diet and obtained both C and N almost exclusively from plant roots.The results indicate that Collembola in the rhizosphere of plants, being assumed to be mainly decomposers, in fact predominately live on plant resources, presumably fine roots or root hairs, i.e. are herbivorous rather than detritivorous or fungivorous. These findings have major implications on the view how plants respond to decomposers in the rhizosphere.
... Being a major component of the soil mesofauna, Collembolans (or 'springtails') are hugely abundant hexapod soil micro-arthropods that have been shown many times to possess strong abilities to regulate decomposition rates of soil organic carbon (SOC) and litter C, through directly altering the accessibility of organic matter (e.g. chewing and diminution), as well as through indirectly controlling the decomposing microflora by trophic interactions (Fox et al., 2006;Kaneda and Kaneko, 2007;Endlweber et al., 2009;Wang et al., 2017). However, different taxa of Collembola have been recognized as herbivorous, detritivorous or fungivorous in different studies (Endlweber et al., 2009;Anslan et al., 2016). ...
... chewing and diminution), as well as through indirectly controlling the decomposing microflora by trophic interactions (Fox et al., 2006;Kaneda and Kaneko, 2007;Endlweber et al., 2009;Wang et al., 2017). However, different taxa of Collembola have been recognized as herbivorous, detritivorous or fungivorous in different studies (Endlweber et al., 2009;Anslan et al., 2016). The dietary habits of Collembola determine the specific role in mediation of the microbial community (i.e., trophic interactions, mutualistic and parasitic relationships) and C mineralization (Anslan et al., 2016). ...
... In agreement with previous ecotoxicological studies by de Lima et al. (2017) andvan Gestel et al. (2017), the observed drastic reduction of Collembolan density and inhibition of its biomass C assimilation (Fig. 2), reflected the high sensitivity of Collembola to neonicotinoid dinotefuran. We also confirmed that Collembola primarily consumed maize and behaved as omnivores (Chamberlain et al., 2006;Endlweber et al., 2009;Anslan et al., 2016), other than exclusive fungivores as suggested by several studies (Tiunov and Scheu, 2005;Wang et al., 2017). Without dinotefuran, Collembola was inferred to synthesize 86.8% and 72.1% of its biomass C from maize in SL and CS, calculated using a 3.5 days C half-life (Fig. 2). ...
Rare studies investigated influence of neonicotinoid insecticides on the whole soil biota including non-target invertebrates and microorganisms. And less is known about the consequent intervention on soil C processes. This study aimed to decipher Collembola-fungi-bacteria interactive effects on pathways of maize C translocation, combining isotopic tracer analysis of relevant compartments with high-throughput sequencing for bacterial and fungal genetic profiles. Dinotefuran was applied at 0 or 100 μg kg⁻¹ (a simulating residual dosage) to microcosms containing soils, Collembola and ¹³C labelled maize. Dinotefuran drastically reduced the density and maize-derived biomass C of Collembola, while intensifying antagonistic associations between soil organisms, with flourishing growth of Ascomycota and Actinobacteria, e.g., Streptomyces. This led to higher soil organic C (SOC) mineralization (elevated by 9.8% to 10.5%) across soils, attributing to the shift in taxonomic and functional guild, e.g., with the increased abundance of genes aligned to cytochrome P450. Maize decomposition was controlled by Collembola that primarily fed on maize, via grazing behavior that facilitated labile maize C preferred decomposers, e.g., Xanthomonadaceae. These findings elucidate the influence of minute dinotefuran on intra-linkages between biomes (Collembola, fungi and bacteria), and highlight such legacy effects on maize and SOC mineralization.
... Collembola heavily rely on root-derived C (Garrett et al., 2001;Larsen et al., 2007;Pollierer et al., 2007;Scheunemann et al., 2015), potentially due to their high preference for root-associated microorganisms (Maboreke et al., 2017;Ostle et al., 2007). Collembola incorporate root-derived C from different channels based on bacteria, fungi, and plants (Crotty et al., 2011;Pollierer et al., 2012), and change diet according to resource availability (Eerpina et al., 2017;Endlweber et al., 2009;Scheunemann et al., 2015). However, determinants of the variation in dietary composition of Collembola between cropping systems and its dependence on differences in microbial resources, especially those utilizing root-derived C, are not well studied. ...
... Collembola switch diet according to the availability of resources (Eerpina et al., 2017;Endlweber et al., 2009;Scheunemann et al., 2015;Sechi et al., 2014). Since Collembola as generalist feeders rely on a wide range of diets (Scheu, 2002), it is reasonable to assume that they shift diet to feed on the most abundant microbial resources depending on cropping system. ...
... Lemanski and Scheu (2014) also found predominance of root feeding in P. armata in grasslands. P. armata and other euedaphic species potentially switch their preference for root C and soil organic C according to the palatability of root resources (Crotty et al., 2011;Endlweber et al., 2009;Scheunemann et al., 2015). ...
Recently fixed plant carbon (C) being released as rhizodeposits is a major resource fueling soil food webs. Soil microorganisms predominate in incorporating root-derived C and subsequently transfer it to higher trophic levels. However, variation in microbial community structure between cropping systems and its consequences for the incorporation of root-derived C into soil microbivores remain unclear. In the present study, we used ¹³CO2 to pulse label a crop monoculture (oilseed rape, Brassica napus L.), a mixed grass community (dominated by Lolium perenne L. mixed with clover Trifolium repens L.), and a young tree plantation (willow, Salix schwerinii E.L. Wolf and Salix viminalis L.). During 28 days, we traced the incorporation of root-derived ¹³C into phospholipid fatty acids (PLFAs) of soil microorganisms and neutral lipid fatty acids (NLFAs) of five Collembola species belonging to three functional groups: epedaphic (surface-dwelling), hemiedaphic (litter-dwelling), and euedaphic (soil-dwelling). The contribution of bacterial and fungal channels to the incorporation of root-derived C into Collembola varied considerably between cropping systems. Collembola incorporated more ¹³C from the bacterial channel in rape than in grass and willow, where fungi were the major C source. This corresponded to a similarly higher ¹³C incorporation into bacterial marker PLFAs in rape as compared to grass and willow. In contrast, while the proportion of bacterial and fungal biomarkers in Collembola NLFAs was related to the ¹³C incorporation into microbial PLFAs, it did not correlate with the proportion of microbial PLFAs in the different cropping systems. This suggests that Collembola rely on specific microbial pools, presumably related to recent plant inputs. Within the same cropping system, hemiedaphic species incorporated more root-derived ¹³C from the bacterial channel compared to euedaphic and epedaphic species. The results demonstrate the remarkable importance of cropping system for the flux of root C into microorganisms and microbivore soil invertebrates. Changes in root C flux into bacterial and fungal resources among cropping systems resulted in differential utilization of these resources by soil microbivores, suggesting that in particular microorganisms fueled by rhizodeposits are vital resources for the nutrition of higher trophic levels in soil food webs.
... Soil fauna have important functions in the transformation of soil organic matter and in nutrient cycling (Carrillo et al. 2011;Wang et al. 2017). Soil collembolans feed on a range of food items including living roots, decomposed plant material, fungi, bacteria, and nematodes, and can thus have substantial effects on the soil ecosystem (Coulibaly et al. 2019;Endlweber et al. 2009;Berg et al. 2004). Collembolans in the soil-plant system can also influence plant growth in various ways such as changing microbial communities, nutrient availability and root traits (Graf et al. 2019;Kuťáková et al. 2018;Ngosong et al. 2014;Endlweber and Scheu 2007;2006). ...
... The internal reference was analyzed with samples after each batch of 10 samples for quality control, and the precision of the 15 N analysis was ˂ 0.10 ‰. The proportion of N incorporated in Collembola, plant shoots and the soil after phytoextraction derived from straw was calculated by a two-source mixing model (Endlweber et al. 2009), and is expressed as F = ( 15 N isotope abundance of sample -15 N isotope abundance of soil before phytoextraction) / ( 15 N isotope abundance of straw -15 N isotope abundance of soil before phytoextraction) × 100. ...
... In the pot experiment the hyperaccumulator may have affected metal uptake by F. candida. The higher Cd concentrations in roots than in soils might have increased the exposure of F. candida which may have directly ingested roots or indirectly ingested microbes on the root surfaces (Eerpina et al. 2017;Endlweber et al. 2009). The positive effects of the hyperaccumulator on the internal metal concentrations of F. candida are also indirectly indicated by the much higher increments in body Cd than in body Pb observed (Table 2) because S. plumbicizincola is a Cdhyperaccumulator but not a Pb-hyperaccumulator (Wu et al. 2013). ...
Aims
There is little information available on the potential influence of soil micro-arthropods on the phytoremediation of metal-contaminated soils using hyperaccumulator plants. We hypothesized that soil micro-arthropods may promote organic matter decomposition, thereby releasing nitrogen and enhancing the growth of and metal uptake by hyperaccumulators and thereby increase phytoextraction efficiency.
Methods
Four highly contaminated soils with a range of metal contents were used in a pot experiment to study the effects of the collembolan Folsomia candida and the mite Hypoaspis aculeifer on phytoextraction by Sedum plumbizincicola, a cadmium (Cd) and zinc (Zn) hyperaccumulator.
Results
Both micro-arthropods survived when the hyperaccumulator grew in the four soils. F. candida slightly increased the growth of S. plumbizincicola and shoot metal concentrations increased significantly in the presence of F. candida with or without H. aculeifer. Soil fauna increased shoot Cd accumulation by 27.9–66.3% compared to corresponding control soils. Similar shoot ¹⁵N abundances across treatments and decreasing shoot N content in two of the soils with addition of F. candida indicate that the promotion of phytoextraction was not associated with increasing plant nitrogen uptake from organic matter by F. candida.
Conclusions
The mechanism of plant growth promotion might be an interaction between the soil fauna and the roots of the hyperaccumulator and this merits further investigation. This work highlights for the first time a potential role of soil micro-arthropods in the phytoextraction of metal-polluted soils.
... For example, Collembola, a dominant soil microarthropod group, is known to regulate flows of nutrients to plants by shaping the biomass and activity of the microbial community (both bacteria and fungi), either directly, through feeding, or indirectly, through the comminution of organic matter and dissemination of microbial propagules (Moore et al., 1988;Coulibaly et al., 2019). Furthermore, various Collembolan species have been shown to act upon plant root biomass without any clear pattern, either directly, by exerting rhizophagous pressure (Endlweber et al., 2009), or indirectly, by interacting with microbes as detailed above. In previous studies, we were able to show that the presence of Collembola stimulates plant growth and accelerate flowering, potentially through increasing nutrient availability and uptake by plants (Forey et al., 2015;Winck et al., 2020). ...
... As Collembola species could only be determined with certainty under a microscope, we selected under the (Gillooly et al., 2001;Mallard et al., 2020) as well as stimulates plant shoot and root biomasses [3] (Lin et al., 2010). Furthermore, presence of Collembola may directly interact with roots by consuming them [4] (Endlweber et al., 2009), but this trophic interaction usually does not detrimentally affect plant performance, as plants seems to rather to increase shoot and root growth in presence of Collembola (Gange, 2000, Partsch et al., 2006, Endlweber and Scheu, 2006, Endlweber and Scheu, 2007, and indirectly through regulation of microflora [5] (Ngosong et al., 2014;Coulibaly et al., 2019;Winck et al., 2020), enhancing mineralization and therefore increasing the pool of soil nutrients [6] (Forey et al., 2015) available for plants or by reducing plant pathogens [7] (Endlweber et al., 2009). Collembola may also directly increase the pool of soil nutrients through their faeces [8] (Hopkin, 1997). ...
... As Collembola species could only be determined with certainty under a microscope, we selected under the (Gillooly et al., 2001;Mallard et al., 2020) as well as stimulates plant shoot and root biomasses [3] (Lin et al., 2010). Furthermore, presence of Collembola may directly interact with roots by consuming them [4] (Endlweber et al., 2009), but this trophic interaction usually does not detrimentally affect plant performance, as plants seems to rather to increase shoot and root growth in presence of Collembola (Gange, 2000, Partsch et al., 2006, Endlweber and Scheu, 2006, Endlweber and Scheu, 2007, and indirectly through regulation of microflora [5] (Ngosong et al., 2014;Coulibaly et al., 2019;Winck et al., 2020), enhancing mineralization and therefore increasing the pool of soil nutrients [6] (Forey et al., 2015) available for plants or by reducing plant pathogens [7] (Endlweber et al., 2009). Collembola may also directly increase the pool of soil nutrients through their faeces [8] (Hopkin, 1997). ...
Soil properties and the growth and maturation of herbaceous plants are known to be influenced by the soil fauna (Collembola) and by the temperature. But little is known about how these two factors interact. We hypothesised that the vegetative and reproductive responses of Poa annua L. to the presence of soil Collembola density will change according to temperature. P. annua was grown in microcosms with or without Collembola at two different air temperature conditions, 16 • C as a Low T • vs. 19 • C as a High T •. Both factors "Collembola" and "Tem-perature" significantly influenced several plant and soil variables. The number of flowers, the root biomass of P. annua were higher either in presence of Collembola or under elevated temperature. The same applied for soil ergosterol or K content for example. Soil nitrate content was exclusively affected by the presence/absence of Collembola and not by the temperature. Finally, significantly interactive effects between temperature and Col-lembola upon several plant or soil variables (root biomass, number of flowers, soil K and Mg content) were shown. Our study suggests that biotic factors (here soil fauna) may strongly interact with climatic variables in regulating plant growth through changes in soil nutrient availability. We provide experimental evidence that climate warming modifies the effect of soil Collembola on the reproduction strategy of the plant.
... Although soil microbes have a direct effect on nutrient mineralization by degrading complex organic compounds such as cellulose and lignin, their composition, structure and activity are often influenced by the presence of animal decomposers such as Collembola and earthworms (Cragg and Bardgett 2001;Ngosong et al. 2004;Eisenhauer et al. 2010;Coulibaly et al. 2019). By feeding on organic residues at different decomposition stages (Endlweber et al. 2009;Chahartaghi et al. 2005) and/or a wide range of soil microbes (Tordoff et al. 2008;Lenoir et al. 2006), soil animal decomposer activity may translate to plant performance by influencing the rates of mineralization and nutrient availability for plants (Scheu et al. 1999; Bardgett and Chan 1999;Partsch et al. 2006;Hedde et al. 2010;Eisenhauer et al. 2011Eisenhauer et al. , 2018Forey et al. 2015). ...
... Besides increase in nutrient availability, presence of Collembola can also enhance plant nutrient uptake by modifying the distribution of nutrients in the rhizosphere (Teuben 1991;Lussenhop 1992), increasing the formation of nutrient-rich patches and changing root morphological variables. As a consequence, plants tend to invest less in their roots when a soil is nutrient-rich (Hodge 2004(Hodge , 2009Endlweber et al. 2009). Those assumptions can explain the higher foliar nutrient contents and the lower root biomass observed in L. perenne growing with Collembola in the present study. ...
... Those assumptions can explain the higher foliar nutrient contents and the lower root biomass observed in L. perenne growing with Collembola in the present study. Similar effects on root variables of collembolan presence were also previously documented (Partsch et al. 2006;Endlweber et al. 2009;Eisenhauer et al. 2011). Lambers et al. (2006 reported that P acquisition could be increased by root traits like root proliferation or increased length of root hairs, enhancing allocation to shallow soil horizons, and mycorrhizal symbiosis. ...
Background and aims
Interactions between functional groups of soil fauna and plants are poorly explored although they drive functional processes such as nutrient availability and therefore plant performance. Here, we investigated the separated and combined effects of two collembolan functional groups on soil properties and growth of Lolium perenne, a typical grass species from temperate grasslands.
Methods
Under microcosm conditions, we established four treatments based on the presence and combination of two collembolan functional groups: (1) control without Collembola; (2) epedaphic species; (3) euedaphic species; (4) epedaphic + euedaphic species. After five months of experiment, we measured the effect of those treatments on both nutritional and morphological variables of L. perenne and on soil properties.
Results
Collembolan presence stimulated plant performance. Individuals of L. perenne growing with euedaphic species presented higher numbers of leaves and nutrient contents compared with individuals growing with epedaphic species. Further, the combination of both collembolan functional groups enhanced plant performance and soil nutrient availability, demonstrating that a functionally diversified soil fauna assemblage cause overyielding of ecological processes.
Conclusion
Our results provide evidences of complementarity interactions between different functional groups of soil fauna causing overyielding of primary production.
... We cannot exclude that Folsomia candida, the Collembola species used in our experiment, may have fed upon roots during the experiment. Collembola in general are known to switch diet and may behave like herbivores in presence of plant roots [30], surely modifying chemicals released from plant roots. For example, root herbivory was shown to influence soil nutrients [31,32]. ...
... Finally, the presence of Collembola can also modify the plant gene expression (RNA) and then the nature and intensity of metabolites exuded by the roots [36][37][38]. In the same manner, the 24 ions showing higher intensities in PC treatment than in P treatment could be attributed to supplementary ions directly provided by the presence of fauna through trophic interactions with the roots for example [30], or indirectly through modified soil microbial communities or root exudates [33,35]. ...
... 2000). Endlweber et al. (2009) showed that P. fimata, and possibly other euedaphic Collembola, are herbivorous rather than herbivorous or faunivorous, in the rhizosphere of plants. Their results indicated that Collembola feed predominantly on fine roots and root hairs in preference to decomposing organic matter, but switch to a fungal/litter diet if plants are absent. ...
... It is therefore possible that cases of poor seedling growth in some crops could be incorrectly attributed to onychiurids, which may have been attracted to already weakened plants attacked by fungal pathogens. Moreover, feeding strategies are also influenced by pH, fertilisers, and root exudates, which are higher in stressed plants (Curl & Truelove 1986;Loranger et al. 2001;Filser 2002;Endlweber & Scheu 2007;Endlweber et al. 2009;Endlweber et al. 2011). Any association of euedaphic Collembola with visible plant damage should be investigated because of the complexities of the soil-plant ecosystem, as other factors may have predisposed the plants to attack. ...
The onychiurid fauna of Australia is revised and found to comprise six species belonging to five genera. All species are already described and are widespread in the Northern Hemisphere so they are considered to be introduced to Australia. For the most part, they are only known in Australia from agricultural and horticultural soils and home gardens as well as worm beds. A dichotomous key to the species is presented together with updated names, relevant synonymies, a brief description of each and comments on their distribution and ecology. The six species separated in the key are Protaphorura fimata (Gisin, 1952), Thalassaphorura encarpata (Denis, 1931), Thalassaphorura cryptopyga (Denis, 1931), Orthonychiurus folsomi (Schäffer, 1900), Deuteraphorura cebennaria (Gisin, 1956) and Onychiurus ambulans (Linnaeus, 1758). A seventh species is listed here but in family Tullbergiidae, Metaphorura affinis (Börner, 1902). It is included as it could be confused with the Onychiurinae in the field. In Australia and overseas, onychiurids have been associated with root damage to plants in home gardens and field crops, and we discuss their pest status using data from assessments of field crop damage in Australia. The aim of this paper is to provide an identification guide to field workers so that they can decide whether control methods are required.
... These studies provided evidence that food sources vary widely among organisms and include living plants and photoautotrophic microorganisms (e.g. cyanobacteria and algae) as well as decayed materials and related saprotrophic microorganisms [6][7][8]. Especially, studies using isotope tracers have revealed the underestimated importance of carbon inputs from living roots into the soil food web [9][10][11][12] and have raised questions over whether soil food webs are really based primarily on detritus. ...
... Differences in stable isotope signatures among these species could reflect differences in their habitat [14] (table 1), leading to differences in the foods they use in addition to root-derived C and the relative proportions of these multiple foods. The stable isotope signatures could also reflect which materials they feed on directly to obtain root-derived C; these include rhizodeposits such as mucilage, mycorrhizal fungi, microorganisms that propagated on the rhizodeposits, and the living root itself, although these sources are still controversial [8,17,40]. ...
Terrestrial carbon cycling is largely mediated by soil food webs. Identifying the carbon source for soil animals has been desired to distinguish their roles in carbon cycling, but it is challenging for small invertebrates at low trophic levels because of methodological limitations. Here, we combined radiocarbon ( ¹⁴ C) analysis with stable isotope analyses ( ¹³ C and ¹⁵ N) to understand feeding habits of soil microarthropods, especially focusing on springtail (Collembola). Most Collembola species exhibited lower Δ ¹⁴ C values than litter regardless of their δ ¹³ C and δ ¹⁵ N signatures, indicating their dependence on young carbon. In contrast with general patterns across all taxonomic groups, we found a significant negative correlation between δ ¹⁵ N and Δ ¹⁴ C values among the edaphic Collembola. This means that the species with higher δ ¹⁵ N values depend on C from more recent photosynthate, which suggests that soil-dwelling species generally feed on mycorrhizae to obtain root-derived C. Many predatory taxa exhibited higher Δ ¹⁴ C values than Collembola but lower than litter, indicating non-negligible effects of collembolan feeding habits on the soil food web. Our study demonstrated the usefulness of radiocarbon analysis, which can untangle the confounding factors that change collembolan δ ¹⁵ N values, clarify animal feeding habits and define the roles of organisms in soil food webs.
... Both Collembola and Oribatida species occupy a gradient of trophic niches spanning several trophic levels according to bulk isotope analyses (Schneider et al. 2004, Chahartaghi et al. 2005, Maraun et al. 2011, Potapov et al. 2016a). In feeding studies, both Collembola and Oribatida can survive, grow, and reproduce on a variety of food sources , Endlweber et al. 2009, Heethoff and Scheu 2016, and Oribatida therefore have been termed "choosy generalists" (Schneider and Maraun 2005). In natural habitats, trophic niches of Collembola and Oribatida are assumed to be rather conserved among species (Schneider et al. 2004, Chahartaghi et al. 2005, Potapov et al. 2016a), but may also shift, for example, in different cropping systems (Li et al. 2020) and forest types (Krause et al. 2019, Maraun et al. 2020. ...
... Ellipses around resource groups are 75% confidence intervals. rely on root-derived carbon (Scheunemann et al. 2015, Pausch et al. 2016, Potapov et al. 2016b, which may be attributed to feeding on roots and on fungi receiving root-derived carbon (Endlweber et al. 2009. Proportions of these resources may shift depending on availability/palatability, for example, in different cropping systems (Li et al. 2020); this presumably is also the case in beech compared to spruce forests, as in the former root-derived resources are particularly important (Cesarz et al. 2013, Zieger et al. 2017. ...
Abstract Soil microarthropods are essential for nutrient cycling in forest ecosystems as they are integral components of decomposer food webs. They channel carbon and nutrients from leaf litter and roots to higher trophic levels; however, knowledge on the relative importance of different channels and on their variation with forest type is lacking. Although the importance of root‐derived inputs for sustaining soil food webs is increasingly recognized, the pathways by which they are channeled to higher trophic levels are little understood. For the channeling, ectomycorrhizal fungi may play a significant role, but until now methods allowing to separate the contribution of ectomycorrhizal and saprotrophic fungi to the nutrition of soil animal communities are lacking. Using dual analysis of 15N and 13C in amino acids (AAs), we investigated trophic positions and basal resources of two major groups of soil microarthropods, Collembola and Oribatida, in beech and spruce forests in Germany. By applying a 13C fingerprinting approach and Bayesian mixing models, we separated in a first step the relative contribution of bacteria, fungi, and plants to the nutrition of soil microarthropods. As fungi were identified as the major food source, in a second step we attempted to separate the contribution of ectomycorrhizal vs. saprotrophic fungi. For the first time, we provide direct evidence that soil microarthropods mainly rely on saprotrophic fungi, whereas ectomycorrhizal fungi are consumed by only few species. While trophic niches of Collembola and Oribatida species generally varied little between beech and spruce forests, plant detritus as basal resource of soil microarthropods was somewhat more important in beech forests, whereas in spruce forests microbial resources dominated. Overall, the dual analysis of carbon and nitrogen in AAs provided insight into food web structure of soil microarthropods in unprecedented detail, and for the first time allowed to estimate the relative importance of mycorrhizal and saprotrophic fungi for soil food web nutrition, a long‐standing riddle in soil food web ecology. The technique provides the perspective for a comprehensive understanding of the trophic structure and energy channeling in soil food webs.
... To our knowledge, there is no literature to date that has comprehensively identified the feeding habits of collembolans because they consume a wide spectrum of resources, including plant roots or litter, different types of soil microbes and metazoan soil fauna (Potapov et al., 2016). Additionally, collembolans can shift their diet from one food resource to another when choices are available (Chahartaghi et al., 2005;Endlweber et al., 2009). This inherently complex feed-ing nature of collembolans makes it difficult to correctly assign them to specific feeding guilds without using isotope tracer techniques. ...
... In our study, most groups classified into herbivores are the facultative feeders. For example, herbivorous collembolans can switch their diet from plant roots to decaying litter (Endlweber et al., 2009). Therefore, we propose that the positive role of herbivores at 0-5 cm in RT and NT soil may partly be due to their manipulation of surface residues by fragmenting and mixing. ...
Long-term (10 years) application of conservation tillage following conversion from conventional tillage (CT) can achieve a new equilibrium in the soil environment, which is vital to reverse soil biodiversity declines and fulfil the goal of maintaining agroecosystem sustainability. However, in such a situation, how the soil community regulates nutrient cycling impacting crop yield is not well documented. Therefore, the relations between mineralized nitrogen (N) delivered by soil food web and soybean (Glycine max Merr.) yield were investigated after 14 years application of CT, reduced tillage (RT) and no tillage (NT) in a black soil (Typic Hapludoll) of Northeast China. We hypothesized that soil mineralizable N would increase with the complexity of the soil food web, and that the trophic groups involved in associating N mineralization with crop yield will vary with soil depth in the conservation tillage practice. During the soybean growing season, soil organisms, including bacteria, fungi, nematodes, mites and collembolans, were extracted and identified monthly from 0–5 and 5–15 cm soil depths to estimate the complexity of the food web indicated by the species richness and connectance indices, and to simulate the mineralized N using energetic food web modelling. The species richness and connectance of
the food web at both soil depths were significantly affected by tillage
practices, and their values decreased of the order of NT > RT > CT. A similar trend was also revealed for the simulated N mineralization, that is, the mineralized N released either from the functional feeding guilds or from the energy pathways of the food web were greater in RT and NT than in CT at both soil depths. Multiple linear regression analysis showed that soil organisms involved in coupling the mineralized N with soybean yield were different at different soil depths, in which fungal and root pathways at 0–5 cm and bacterial pathway at 5–15 cm were the driving factors for the supply of mineralized N to soybean in NT and RT soils. These results support our hypothesis and highlight the essential role of soil food web complexity in coupling N mineralization and crop yield after long-term application of conservation tillage. Additionally, the current modelling work provides basic hypotheses for future studies to test the impact of soil biodiversity or specific functional guilds on the fate of N in agro-ecosystems.
... Alternatively, if all diet components are of sufficiently high quality, synergistic net-positive effects due to optimizing the nutrient profile (Rapport 1980) are expected. These responses should further differ in intensity between species as their habitat changes from above-ground epedaphic to below-ground euedaphic Collembola, as below-ground species are generally better adapted to varying diet sources due to the heterogeneity and food scarcity of their habitat (Ponge, 2000;Endlweber et al., 2009). ...
... Such variation in effect strength may be a result of habitat (Ponge, 2000), with epedaphic species (L. violaceus) being less adapted to resource heterogeneity in comparison to food generalists with opportunistic lifestyles residing at greater soil depth, with more heterogenic food availability and quality (Jørgensen et al., 2003;Larsen et al., 2008;Endlweber et al., 2009). Moreover, P. fimata and F. candida primarily allocate nutrients into growth (Larsen et al., 2009(Larsen et al., , 2011, which corresponds to the present results, with diet quality primarily important for biomass gain. ...
The effect of food resources, varying in C/N ratio, lipid and ω3 polyunsaturated fatty acid (ω3-PUFA) content, on the fitness of three Collembola species (the euedaphic Protaphorura fimata, hemiedpahic Folsomia candida and epedaphic Lepidocyrtus violaceus) was investigated. Dietary routing of fatty acids served as an indicator for resource consumption and assimilation. Laboratory feeding experiments were performed with single and mixed diets made from algae, cyanobacteria, fungi, soil bacteria or plant roots and leaves. Collembola exhibited species-specific responses in biomass and survival rate to the diets differing in quality, reflecting adaptations to their soil environment. Generally, wide dietary C/N ratios had a negative impact, with roots especially unfavorable, while the dependence on ω3-PUFAs varied. Mixing diets did mostly result in intermediate results where high-quality resources compensate for low-quality resources, with only mixes of resources favoured by Collembola in the wild showing synergistic positive effects. The results suggest that most resources of soil detritivores, irrespective of green or brown food chain, represent a non-optimal diet, with clear adaptations depending on habitat and the potential to truly exploit any resource mostly exhibited in euedaphic species.
... Due to closer association with roots, euedaphic Collembola inhabiting the mineral soil presumably incorporate more root-derived C than hemiedaphic and epedaphic Collembola, which preferentially colonize organic layers or the soil surface (Scheunemann et al. 2010;Potapov et al. 2016a). However, incorporation of rootderived C by different functional groups may differ between cropping systems due to trophic plasticity of Collembola species Endlweber et al. 2009;Scheunemann et al. 2015;Eerpina et al. 2017). ...
... This may especially be true for P. armata, since its natural abundance δ 13 C values decreased from comparatively high values in rape and willow to low values in grass (Table S4), indicating a more direct trophic relationship to grass roots, presumably via feeding on roots, arbuscular mycorrhizal fungi, or root-feeding nematodes. Previous studies also found euedaphic Collembola species to shift their food preference from root C to soil organic C depending on resource availability (Gillet and Ponge 2003;Endlweber et al. 2009;Eerpina et al. 2017). In addition, high belowground C allocation in grass may promote its utilization by different functional groups of Collembola as well as their microbial prey. ...
As the dynamics and magnitude of rhizodeposition vary considerably among cropping systems, we investigated effects of cropping system on the incorporation of root-derived carbon (C) into Collembola, a dominant taxon of soil microarthropods. In the field, we used 13 CO 2 to pulse label a crop monoculture (oilseed rape, Brassica napus L.), a mixed-grass community (dominated by Lolium perenne L. mixed with clover Trifolium repens L.), and a tree plantation (willow, Salix schwerinii E.L. Wolf and Salix viminalis L.). During 28 days, the incorporation of 13 C was traced in nine species of Collembola including epedaphic (surface-dwelling), hemiedaphic (litter-dwelling), and euedaphic (soil-dwelling) functional groups. Incorporation of 13 C into Collembola reached a plateau before day 3 after the labeling in grass and willow, but increased up to day 14 in rape. While euedaphic Collembola incorporated less root-derived C than epedaphic and hemiedaphic Collembola in rape and willow, the incorporation of 13 C was similar among functional groups in grass. Differential incorporation of 13 C in euedaphic species points to niche differentiation within the same functional group. Our findings highlight that cropping system not only affects the flux of root C into soil mesofauna, being slower in rape than in grass and willow, but also the utilization of root-derived resources by functional groups and species of Collembola. The results indicate that pronounced differences in belowground C inputs between cropping systems affect microbivores as basal species and thereby soil food webs and their functioning and services.
... The presence of this feces changes the composition of the microbial community in the soil [42,43], which in turn changes the allocation of its food resources, leading to changes in the Acari and Collembola communities. Acari and Collembola have a wide range of dietary habits [34,85], and the presence of leaf litter and the abundance of fungi provide abundant food resources for Acari and Collembola that feed on detritus and fungi [86]. The mite species Acrogalumna shogranensis, which was dominant throughout the experiments, had a strong susceptibility to millipede activity ( Figure 2; and Tables S3 and S4). ...
Ecosystem engineers influence the structure and function of soil food webs through non-trophic interactions. The activity of large soil animals, such as earthworms, has a significant impact on the soil microarthropod community. However, the influence of millipedes on soil microarthropod communities remains largely unknown. In this microcosm experiment, we examined the effects of adding, removing, and restricting millipede activity on Acari and Collembola communities in litter and soil by conducting two destructive sampling sessions on days 10 and 30, respectively. At the time of the first sampling event (10 d), Acari and Collembola abundance was shown to increase and the alpha diversity went higher in the treatments with millipedes. At the time of the second sampling event (30 d), millipedes significantly reduced the Collembola abundance and alpha diversity. The results were even more pronounced as the millipedes moved through the soil, which caused the collembolans to be more inclined to inhabit the litter, which in turn resulted in the increase in the abundance and diversity of Acari in the soil. The rapid growth of Collembola in the absence of millipedes significantly inhibited the abundance of Acari. The presence of millipedes altered the community structure of Acari and Collembola, leading to a stronger correlation between the two communities. Changes in these communities were driven by the dominant taxa of Acari and Collembola. These findings suggest that millipedes, as key ecosystem engineers, have varying impacts on different soil microarthropods. This study enhances our understanding of biological interactions and offers a theoretical foundation for soil biodiversity conservation.
... Many groups of soil invertebrates have been proposed as indicators of soil health, and their sensitivity to the presence of chemicals in soil has been used to estimate the risk of specific elements in soil. Among these bioindicators are the collembolans (Cortet et al. 1999); these invertebrates play an important role in several ecosystem services, since they contribute to organic matter decomposition, are a food source for other soil fauna, transport bacteria and fungi in soils, and may increase the allocation of nutrients to plants, bringing benefits to soil health (Hopkin 1997;Nakamori et al. 2008;Endlweber et al. 2009). According to their life form and distribution in soil, collembolans can be classified as epigeic (living on plant litter and soil surface), hemiedaphic (between the surface and on soil), and euedaphic (living on soil) (Oliveira Filho and Baretta 2016). ...
Laboratory ecotoxicological tests are important tools for the management of environmental changes derived from anthropogenic activities. Folsomia candida is usually the model species used in some procedures. However, this species may not be sufficiently representative of the sensitivity of the other collembolan species. This study aimed to evaluate (i) the effects of soils naturally rich in potentially toxic elements (PTE) and soil characteristics on the reproduction and survival of different collembolan species, (ii) whether the habitat function of these soils is compromised, and (iii) to what extent F. candida is representative of the other collembolan species. For this, reproduction tests with six collembolan species were conducted in 14 different samples of soils. In general, collembolan reproduction was not completely inhibited in none of the natural tested soils. Even soils with high pollution load index values did not negatively affect collembolan reproduction for most of the species. In contrast, the lowest collembolan reproduction rates were found in a visually dense soil (lowest volume/weight ratio), highlighting that soil attributes other than total PTE concentration also interfere in the reproduction of collembolans. Our results support the idea that the F. candida species might not be representative of other collembolan species and that laboratory tests to assess soil contaminations should be conducted using diverse collembolan species.
... Root-derived carbon represents the primary source of organic matter in soil and fuels belowground food webs (Bradford, 2016;Pollierer et al., 2023;. In particular microarthropods inhabiting the soil, such as many oribatid mites and springtails, heavily rely on resources derived from roots (Remén et al., 2008;Endlweber et al., 2009;Potapov et al., 2016;Bluhm et al., 2021). In addition, plant roots shape important habitat characteristics of soil microarthropods such as soil structure and soil moisture (Gould et al., 2016). ...
Biodiversity is declining on a global scale with detrimental effects on ecosystem functioning. Effects of reduced tree diversity on the diversity of aboveground animals have been studied in detail, whereas the response of soil animals remains poorly understood. We analyzed seasonal variations of soil oribatid mite communities as major soil detritivores along a tree diversity gradient as implemented in the Biodiversity-Ecosystem Functioning Experiment in China. A total of 24,898 oribatid mites were collected over two years and eight sampling periods. Generally, density and species richness of oribatid mites significantly differed among the four seasons and were highest in winter. By contrast, tree diversity did not significantly affect the density and species richness of oribatid mites as main factor, but its effect varied with season, however, the variations were generally small. Also, oribatid mite community composition varied with seasons but not significantly with tree diversity. Further, functional traits and functional diversity of oribatid mites significantly changed with seasons, but this varied with tree diversity although these variations were small. Overall, the effect of season on soil oribatid mite communities considerably exceeded that of tree diversity, indicating that oribatid mite communities in soil are mainly structured by seasonal variations in abiotic factors and resources outweighing the role of tree diversity. The results highlight the necessity of considering temporal variations when analyzing relationships between plant diversity and soil animal communities.
... Springtails feed on SOM [63] and soil microorganisms [55], suggesting that the high SOM soil provided a greater food supply than the others in our experiment. This was confirmed because, in five of seven treatment levels, springtail activity was higher in the high SOM soil. ...
Glyphosate is the most widely used active ingredient (AI) in glyphosate-based herbicides (GBHs) worldwide and is also known to affect a variety of soil organisms. However, we know little about how the effects of glyphosate AIs differ from those of GBHs that also contain so-called inert co-formulants. We conducted a greenhouse experiment using the model cover crop white mustard (Sinapis alba) to investigate the effects of three GBHs (Roundup PowerFlex, Roundup LB Plus, and Touchdown Quattro) and their respective glyphosate AIs (glyphosate potassium, isopropylamine, and diammonium salt) on epedaphic springtails (Sminthurinus niger; Collembola) activity in soils with low (3.0%) or high (4.1%) organic matter content (SOM). Springtail activity was assessed using pitfall traps. Most GBHs and AIs reduced springtail activity compared to mechanical removal of mustard in the short-term and even up to 5 months after application. GBHs and AIs differed considerably in their effects on springtail activity, and effects were modified by SOM content. Our results highlight the need to (i) distinguish between the effects of glyphosate AIs and commercial GBH formulations, (ii) disclose all ingredients of GBHs, as co-formulants also affect non-target organisms, and (iii) include soil properties in ecotoxicological risk assessments for soil organisms to better characterize the situation in the field.
... First, paleontological emphasis is unavoidably on the fossils: the gazelles and grasshoppers. However, nematodes can be herbivores (Blaxter, 2011;Kiontke and Fitch, 2013;Potapov et al., 2022); so, too, can tardigrades, symphylan myriapods, and collembolan hexapods (Eltoum and Berry, 1985;Endlweber et al., 2009;Schill et al., 2011;Potapov et al., 2022). Herbivorous mites do receive consideration in fossil leaf damage studies as possible culprits for some galls (Labandeira et al., 2007b), but mites can also feed on plant tissues in more varied ways (Labandeira et al., 2014;Potapov et al., 2022). ...
Direct fossil preservation of leaf damage, arthropod mouthparts, and vertebrate teeth has understandably led to a focus on oral processing of plant material when considering the evolution of herbivory in deep time. Here, nutrient stoichiometry is advocated as an important alternative constraint on the evolution of herbivory. Most life possesses C:N ratios of approximately 7:1, but uniquely among land plants, that ratio can be skewed to 1,000:1 in some tissues due to the abundance of cell wall structural polymers that lack nitrogen entirely. Since the superabundance of carbon is unevenly distributed between and within plant organs and tissues, avoidance is a viable strategy for herbivores, but availability is dependent on herbivore body size. Sub-millimeter herbivores can attack plants cell-by-cell, avoiding cell wall consumption entirely in favor of cell contents, thereby presenting little stoichiometric distinction between herbivory and consumption of animals, fungi, or unicellular life. Insect-sized herbivory at least allows avoidance of the most carbon-rich/nutrient-poor tissues within a plant organ. However, vertebrate sizes prevent such selectivity. The increasing challenges of nutrient stoichiometry with increasing herbivore body size are recapitulated through time in the fossil record. The first herbivores were microherbivores that can avoid cell wall consumption—present already with their first opportunity for fossil preservation in the Early Devonian. Tissue-specific consumption by insect herbivores followed in the Carboniferous. One hundred fifty million years would pass after the first microherbivory record before vertebrate herbivory would reach its modern prevalence.
... And yet, soil fauna can directly and indirectly regulate soil bacterial and fungal communities. Nematodes grazing of bacterial or fungal cells directly shifts the microbial community [11], whereas collembolans feeding on plant secondary roots can indirectly stimulate the growth of specific microbes in the rhizosphere [12][13][14]. Similarly, earthworms change soil physicochemical characteristics by degrading organic matter, turning over nutrients, and oxygenating soil, thereby indirectly shifting the microbial community [15][16][17][18]. ...
The aim of this study was to determine whether the soil faunal-microbial interaction complexity (SFMIC) is a significant factor influencing the soil microbial communities and the willow growth in the context of PAH contamination. The SFMIC treatment had eight levels: just the microbial community, or the microbial community with nematodes, springtails, earthworms and all the possible combinations. SFMIC affected the height and biomass of willows after eight weeks or growth. SFMIC affected the structure and the composition of the bacterial, archaeal and fungal communities, with significant effects of SFMIC on the relative abundance of fungal genera such as Sphaerosporella , a known willow symbiont during phytoremediation, and bacterial phyla such as Actinobacteriota , containing many polycyclic aromatic hydrocarbons (PAH) degraders. These SFMIC effects on microbial communities were not clearly reflected in the community structure and abundance of PAH degraders, even though some degraders related to Actinobacteriota and the diversity of Gram-negative degraders were affected by the SFMIC treatments. Over 95% of PAH was degraded in all pots at the end of the experiment. Overall, our results suggest that, under our experimental conditions, SFMIC changes willow phytoremediation outcomes.
... Many species of soil-living Collembola are believed to be mycophagous, although their food resources vary greatly depending on the taxonomic affinity, life form, and preferred habitats in the soil profile [20,21]. Many species of Collembola are opportunistic in their feeding habits and adjust their diet depending on the availability and quality of the resources, including living plant roots and mycorrhizae [22][23][24][25]. This can explain, in part, the controversial results discussed above. ...
Ectomycorrhizal fungi are a prominent component of the soil biota of boreal forests, but the role of mycorrhizal mycelium as a food source for soil Collembola remains controversial. We addressed this question in a trenching experiment in young (70 years old) and old (180 years old) stands of Scotch pine, combined with stable isotope analysis. Trenching halved the biomass of ectomycorrhizal mycelium, estimated using in-growth mesh bags. In the young forest, the abundance of two euedaphic Collembola species, Mesaphorura yosiii and Willemia anophthalma, decreased after trenching by 99 and 97% respectively, while in the old forest the abundance of Collembola was not affected. In both forests, trenching reduced δ15N values of the dominant euedaphic species Isotomiella minor and W. anophthalma, indicating a shift in trophic niches. Thus, we obtained convincing evidence of species-specific trophic links of euedaphic Collembola species to the mycelium of mycorrhizal fungi.
... The mechanism driving this may be differences in plant structure between the two species. Collembola prefer fine plant roots when feeding (Endlweber et al. 2009), and P. arundinacea is a stoloniferous species, producing many adventitious fine roots along stems for establishing new growth (Kidd 2017). This is not the case for C. lyngbyei, meaning there is likely a greater density of aboveground root biomass in P. arundinacea plant communities (Kidd 2017) available for colonization by Collembola. ...
Invasive plants can impact ecosystem services, such as by reducing availability of nutritional resources for detritivorous arthropods that are valued for juvenile fish production. We compared invasive reed canarygrass (Phalaris arundinacea) and native Lyngbye's sedge (Carex lyngbyei) stands along the lower Columbia River, focusing on their contributions to juvenile salmon prey resources. Controlling for environmental factors such as river reach, elevation, and hydrology, we sampled invertebrates from fallout traps, emergence traps, benthic cores, and litter bags in emergent wetland habitats dominated by either P. arundinacea or C. lyngbyei. In litter bags macrodetritus quantity, quality, and decay rates were also quantified. Detritus quality measured by the carbon to nitrogen ratio, was higher from C. lyngbyei suggesting that it produces more and higher quality detritus during the time when juvenile salmonids occupy the area. The abundance and biomass of combined invertebrates in fallout and emergence traps were similar between the vegetation types, but in benthic cores overall invertebrate abundance was greater in C. lyngbyei. Densities of the salmon prey groups total dipteran insects and Chironomidae from fallout traps and benthic cores, and the biomass from fallout traps were greater in C. lyngbyei. Emergent Diptera and Chironomidae abundance and biomass were similar between the vegetation types. Overall macroinvertebrate assemblage and diversity was not affected by P. arundinacea, but the salmon prey taxa Diptera and Chironomidae were reduced in P. arundinacea. It is unknown whether the difference between the two vegetation types is of a magnitude that affects juvenile Chinook salmon trophic function. Additional studies including a comparison to juvenile salmon insect consumption would contribute to reducing uncertainty.
... Springtails and tardigrades on the Forni Glacier are herbivorous/detritivorous groups (Guidetti et al. 2012;Hao et al. 2020) which likely utilize algae and detritus (organic matter, microbes), as described in their non-glacier counterparts (Bryndová et al. 2020;Endlweber et al. 2009;Hao et al. 2020;Rusek 1998). Results of carbon and nitrogen isotopic analyses showed that springtails had higher δ 13 C and δ 15 N values compared to tardigrades. ...
Glacier surfaces are the most biologically productive parts of glaciers with a variety of organisms and habitats. However, distinctiveness of habitats and communities of dominant invertebrate consumers on the ice surface is poorly documented. We focused on dominant consumers in three supraglacial (on the glacier surface) habitats on the alpine glacier Forni-cryoconite holes (water-filled reservoirs with a thin layer of sediment at the bottom), supraglacial debris (layer of stones and gravel covering glacier surface), and surface ice of the weathering crust. We analyzed carbon and nitrogen contents and stable isotope ratios (δ 13 C, δ 15 N), organic matter (OM) content, biomass of consumers, and the community composition of consumers to investigate differences between supraglacial habitats. In cryoconite holes, tardigrades (Tardigrada) were dominant consumers. In supraglacial debris, only springtails (Collembola) occurred mainly between stones and ice. No active animals were found in the surface ice of the weathering crust. Carbon and nitrogen contents, δ 13 C, and δ 15 N of invertebrates and OM differed between habitats. Cryoconite was enriched in OM with high δ 13 C and low δ 15 N compared to supraglacial debris likely indicating differences in major components of OM serving as food of invertebrates. Also, the OM, and carbon and nitrogen contents differed between habitats with the highest concentration in cryoconite. The dry biomass of tardigrades was similar compared to springtails. We present the first observation of differences between supraglacial habitats in the Alps based on the community composition of invertebrates, OM and stable isotopes. This initial study highlights the importance of differences in habitats and its consumers in the functioning of supraglacial ecosystem.
... The amount of direct interaction between plants and soil microarthropods is not well understood. Some research suggests that when plant roots are present, Collembola switch their diet almost exclusively to roots or root-derived products (Endlweber et al. 2009). Though in many experiments it has proven difficult to distinguish among roots, rhizodeposits, and root-associated microbes as the actual food source for Collembola (Eerpina et al. 2017). ...
Background
Soil microarthropods influence many soil processes that support plant growth and development.
Scope
In this paper we review the current understanding of direct microarthropod-plant interactions, how microarthropod-microbe interactions indirectly impact plant growth, and key areas for future study.
Conclusion
Microarthropod impacts on plants are primarily routed through their interactions with microbial communities, mediating organic matter decomposition, nutrient cycling and allocation, and plant-pathogen dynamics in soils. The research investigating how microarthropod-saprotrophic microbe interactions affect plants through decomposition and nutrient cycling indicates a generally positive relationship, though this relationship is influenced by the overall diversity or species richness observed in the microarthropod communities. The effects of microarthropod-plant symbionts interactions on plants are varied and there is no clear benefit or detriment to plants via this mechanism. The effects of microarthropod-plant pathogen interactions on plants suggest that, in most cases, microarthropods will reduce disease incidence and severity. The limited diversity of the study taxa in this area of research is a major limitation to our understanding of how microarthropods impact plant health. Our review revealed that while much is known about microarthropod impacts on the intermediate processes that influence plants, only a subset of studies have quantified plant responses to microarthropod activity. Overall, existing evidence indicates that the overall effects of microarthropods on plants is positive. Future research should aim to incorporate more plant metrics and consider both microarthropod and microbial community dynamics in designed and observational studies.
... Lower richness of microbes and higher abundance of nematodes were found in the maize rhizosphere compared to unplanted soil (Matus-Acuña et al., 2021;Szoboszlay et al., 2015). Both studies further mentioned that having plant roots in soil is more attractive for soil fauna, including the arthropods that rely on carbon sources released from roots (Curry and Ganley, 1977;Endlweber et al., 2009;Sabais et al., 2011;Scheunemann et al., 2015). Indeed, low diversity of arthropods was apparent in the control plot, where food resources were lacking after maize planting. ...
While ecological roles of rhizosphere arthropods are well documented, little is known about the relationship between the development of plant roots and soil arthropod communities in agroecosystems. In this study, we investigated the effects of maize varieties and their root traits on the diversity and community composition of soil arthropods over time. Soil arthropods and root traits were evaluated before planting and at 30 and 60 days after planting in four maize varieties with different root growth angles and lateral root branching. Arthropod diversity declined from day 0 to 30 but recovered by day 60 with the development of maize roots. Two maize varieties (Nei 542018 and Nei 542022) exhibited lower brace and crown root angles, and arthropod taxon richness was greater in these two varieties than in others. The highest abundance of detritivores and predators was found in one of the maize varieties (Nei 542018) which, in addition to lower root angle, attained greater root diameter and lateral root branching and length. Redundancy analysis indicated that soil arthropod composition was correlated with crown root angle. Our findings highlight the importance of root traits, especially the angle of the roots, to enhance arthropod biodiversity in the rhizosphere ecosystem.
... For example, in temperate forests the importance of root resources for arthropods, earthworms and fungivorous nematodes may exceed that of litter resources (Pollierer et al. 2007(Pollierer et al. , 2012Gilbert et al. 2014;Kudrin et al. 2021), whereas in subtropical plantations litter resources have been found to be more important than root resources for earthworms (Chen et al. 2020). Also, in temperate forests oppiid mites, onychiurid springtails, proturans, and centipedes have been found to heavily rely on root-derived resources (Remén et al. 2008;Endlweber et al. 2009;Goncharovet al. 2016;Potapov et al. 2016b;Bluhm et al.2019b). However, the relative importance of these two pathways in fuelling soil food webs and its variation among forest types and biomes remain unclear. ...
Belowground life is traditionally considered to rely on leaf litter as the main basal resource, whereas the importance of roots remains little understood, especially in the tropics. Here, we analysed the response of 30 soil animal groups to root trenching and litter removal in rainforest and plantations in Sumatra and found that roots are similarly important to soil fauna as litter. Trenching effects were stronger in soil than in litter with animal abundance being overall decreased by 42% in rainforest and by 30% in plantations. Litter removal little affected animals in soil, but decreased the total abundance by 60% both in rainforest and rubber plantations but not in oil palm plantations. Litter and root effects were explained either by the body size or vertical distribution of specific animal groups. Our findings highlight the importance of root-derived resources for soil animals and quantify principle carbon pathways in tropical soil food webs.
... The enemy-release hypothesis poses that alien plants are released from most of their specialist natural enemies (Keane & Crawley, 2002;Liu & Stiling, 2006;Mitchell & Power, 2003;Vilà et al., 2005). Following this logic, alien plants should be damaged less than natives by root herbivores, such as some Collembola taxa belonging to the families Onychiuridae and Sminthiridae (Chahartaghi et al., 2005;Endlweber et al., 2009). ...
Although many studies have tested the direct effects of drought on alien plant invasion, less is known about whether drought affects alien plant invasion indirectly via interactions of plants with other groups of organisms such as soil mesofauna.
To test for such indirect effects, we grew single plants of nine naturalized alien target species in pot mesocosms with a community of five native grassland species under four combinations of two drought (well‐watered vs. drought) and two soil‐mesofauna inoculation (with vs. without) treatments.
We found that drought decreased the absolute and the relative biomass production of the alien plants, and thus reduced their competitive strength in the native community. Drought also decreased the abundance of soil mesofauna, particularly soil mites, but did not affect the abundance and richness of soil herbivores. Soil‐fauna inoculation did not affect the biomass of the alien plants but increased the biomass of the native plant community, and thereby decreased the relative biomass production of the alien plants. This increased invasion resistance due to soil fauna, however, tended (p = 0.09) to be stronger for plants growing under well‐watered conditions than under drought.
Synthesis. Our multispecies experiment thus shows that soil fauna might help native communities to resist alien plant invasions, but that this effect might be weakened under drought. In other words, soil mesofauna may buffer the negative effects of drought on alien plant invasions.
... Thus, a reduction in niche width under the effect of nutrient addition may result from changes in the availability of FFC sources. Collembola may switch their diet if resources become scarce or if more palatable resources become available (Endlweber et al., 2009;Scheu and Folger, 2004). For instance, assessment of Collembola for root-derived resources may change depending on the vegetation type (Li et al., 2020). ...
Ecosystems worldwide are being subjected to increasing rates of nutrient deposition. Additional nitrogen (N) and phosphorus (P) inputs and liming are common practices in agroecosystems that have long-term consequences for plant and microbial diversity and community structure during ecosystem restoration. However, legacy effects of nutrient deposition on multitrophic biodiversity and trophic interactions of soil organisms are poorly understood. Collembola is a good model group to study such effects. These small soil invertebrates are intimately linked to plants and microbes, and play an important role in soils by supporting soil fertility and energy channeling to higher trophic levels in soil food webs. Here, we studied the trophic niche structure of epigeic Collembola during a long-term (20 years) nutrient addition experiment in the Central Brazilian savanna (Cerrado), one of the tropical agricultural frontiers. We used descriptive isotopic metrics of Collembola communities based on stable isotopes of carbon and nitrogen to evaluate the legacy effects of fertilization (with N, P, and N + P additions) and liming on their trophic-niche structure. The strongest trophic niche shifts were observed under N addition, manifested in the form of (i) a reduction in trophic niche widthsingle bondthat is, decreased diversity of consumed basal resources available to the Collembola communitysingle bondand (ii) in a more even distribution of Collembola taxa in trophic space. Community trophic niche was strongly displaced under P, N + P, and liming additions (i.e., it did not overlap with the control), reflecting intensified trophic links of Collembola to exotic C4 grasses. Overall, our results indicate that increased atmospheric N deposition simplifies the trophic structure of Collembola communities, which may affect the efficiency and pathways of energy channeling in soil food webs and soil functioning. In addition, the observed niche shifts suggests the need for flexibility in feeding by soil animals in savanna to persist under supplemental N + P and liming. Our study is among the first to explore the trophic structure of invertebrates in tropical soils and provides further evidence that nutrient deposition and agricultural fertilization and liming legacy effects have long-term consequences for soil organisms on multiple trophic levels.
... Numerically dominant species in most ecosystems are represented by the hemiedaphic life form and these species were shown to decline in the absence of root carbon (Fujii, Saitoh & Takeda, 2014). Close link to root carbon was repeatedly suggested for Onychiuridae, a soil-adapted family of Collembola (Endlweber, Ruess & Scheu, 2009;Fujii et al., 2016;Potapov et al., 2016a). However, the exact mechanisms of the trophic link between roots and Collembola remain unclear. ...
Soil organisms drive major ecosystem functions by mineralising carbon and releasing nutrients during decomposition processes, which supports plant growth, aboveground biodiversity and, ultimately, human nutrition. Soil ecologists often operate with functional groups to infer the effects of individual taxa on ecosystem functions and services. Simultaneous assessment of the functional roles of multiple taxa is possible using food-web reconstructions, but our knowledge of the feeding habits of many taxa is insufficient and often based on limited evidence. Over the last two decades, molecular, biochemical and isotopic tools have improved our understanding of the feeding habits of various soil organisms, yet this knowledge is still to be synthesised into a common functional framework. Here, we provide a comprehensive review of the feeding habits of consumers in soil, including protists, micro-, meso-and macrofauna (invertebrates), and soil-associated vertebrates. We have integrated existing functional group classifications with findings gained with novel methods and compiled an overarching classification across taxa focusing on key universal traits such as food resource preferences, body masses, microhabitat specialisation, protection and hunting mechanisms. Our summary highlights various strands of evidence that many functional groups commonly used in soil ecology and food-web models are feeding on multiple types of food resources. In many cases, omnivory is observed down to the species level of taxonomic resolution, challenging realism of traditional soil food-web models based on distinct resource-based energy channels. Novel methods, such as stable isotope, fatty acid and DNA gut content analyses, have revealed previously hidden facets of tro-phic relationships of soil consumers, such as food assimilation, multichannel feeding across trophic levels, hidden trophic niche differentiation and the importance of alternative food/prey, as well as energy transfers across ecosystem compartments. Wider adoption of such tools and the development of open interoperable platforms that assemble morphological, ecological and trophic data as traits of soil taxa will enable the refinement and expansion of the multifunctional classification of consumers in soil. The compiled multifunctional classification of soil-associated consumers will serve as a reference for ecologists working with biodiversity changes and biodiversity-ecosystem functioning relationships, making soil food-web research more accessible and reproducible.
... Collembolans spanning a range of trophic niches might benefit from resources provided directly or indirectly by grass roots, litter, or arbuscular mycorrhizal fungi (Ngosong et al., 2014). Some herbo-fungivorous collembolans may prefer roots over fungal hyphae when given a choice (Endlweber et al., 2009), and grass roots, which tend to be poorly-defended in comparison to conifer roots, could be especially palatable. A meta-analysis of studies examining nematode trophic groups indicated that energy flow through the herbivory channel is greater in grassland than in forest soil food webs (Zhao and Neher, 2014). ...
Thinning, mastication, and prescribed fire are restoration treatments frequently employed in unnaturally dense second-growth Pinus ponderosa forests of the Western United States. Although a goal of these treatments is to restore ecosystem structure and function, little information is available regarding treatment effects on soil micro- and mesofauna, which comprise the overwhelming majority of metazoan forest inhabitants and occupy key positions in soil food webs. We quantified nematodes, mites, and collembolans in soil and litter habitats within untreated control, thinned (comprising thinning and masticating wood), and burned (comprising thinning and masticating, followed by broadcast burn) in P. ponderosa forest management units at Valles Caldera National Preserve in New Mexico, USA. We linked patterns in animal abundance to resource and habitat characteristics, hypothesizing that resources and available habitat for many taxa would increase with thinning and decrease with burning. Two years after thinning, densities of collembolans and nematodes in the thinned unit were higher than in the untreated control unit, but one year post-fire, their densities in the burned unit were similar to those of the untreated control unit. Mite abundance, however, was not elevated in the thinned unit and was lower in the burned unit. Although faunal communities were highly heterogeneous, a significant proportion of the variance in faunal abundances was explained by easily and inexpensively measured habitat and resource characteristics: bulk density, soil organic matter (SOM), pH, grass cover, and litter cover and depth. These findings demonstrate the abiotic and biotic factors that structure faunal habitats so that forest managers have a more complete understanding of the impacts of forest restoration treatments.
... inhibits EM formation of forest trees 26,30 , causes a reduction of the rhizosphere microbial biomass 31 and a reduction in root growth 32 . The springtail P. armata can acquire nutrients from litter, but in presence of plant roots they may switch diet and obtain both C and N almost exclusively from plant roots 33 . 34 , but since the grazing may stimulate compensatory growth of the hyphae, mycelial biomass may not decrease but even increase due to moderate grazing 29,35 . ...
Endogenous rhythmic growth (ERG) is displayed by many tropical and some major temperate tree species and characterized by alternating root and shoot flushes (RF and SF). These flushes occur parallel to changes in biomass partitioning and in allocation of recently assimilated carbon and nitrogen. To address how biotic interactions interplay with ERG, we cross-compared the RF/SF shifts in oak microcuttings in the presence of pathogens, consumers and a mycorrhiza helper bacterium, without and with an ectomycorrhizal fungus (EMF), and present a synthesis of the observations. The typical increase in carbon allocation to sink leaves during SF did not occur in the presence of root or leaf pathogens, and the increase in nitrogen allocation to lateral roots during RF did not occur with the pathogens. The RF/SF shifts in resource allocation were mostly restored upon additional interaction with the EMF. Its presence led to increased resource allocation to principal roots during RF, also when the oaks were inoculated additionally with other interactors. The interactors affected the alternating, rhythmic growth and resource allocation shifts between shoots and roots. The restoring role of the EMF on RF/SF changes in parallel to the corresponding enhanced carbon and nitrogen allocation to sink tissues suggests that the EMF is supporting plants in maintaining the ERG.
... Moreover some Collembola, assumed to be mainly decomposers, switch their diet in the presence of plant roots, especially fine roots, and may obtain carbon and nitrogen almost exclusively from plant roots (Eerpina et al., 2017;Endlweber et al., 2009). In the same way, an increase in the sensitivity of wheat varieties to septoria leaf blotch, may increase food resources for fungal-feeding collembolan species (Friberg et al., 2005;Jorgensen et al., 2005;Ponge, 1988). ...
The genetic diversity of cultivated crops has decreased continuously since the beginning of the 20th century, because of the gradual replacement of genetically heterogeneous traditional varieties by new genetically homogenous varieties, grown in monospecific stands. The resulting agro-ecosystems are now considered as unsustainable. Increasing within-field genetic crop diversity by using a mixture of varieties could increase the sustainability of these agro-ecosystems. This could also potentially increase non-crop biodiversity. In the present study we used an experimental approach to (1) test whether the number of wheat varieties (genetic diversity), the number of functional groups (functional diversity), the composition of functional groups and wheat traits influence 1) species richness and abundance of Collembola, and (2) species and trait assemblages of Collembola. A total of 104 plots were seeded with either monocultures or mixtures of 2, 4 and 8 wheat varieties. Soil cores were collected in each plot to extract Collembola and measure soil features. Wheat variety number and functional wheat diversity did not impact abundance and species richness of Collembola. The sensitivity of wheat to septoria leaf blotch was positively related to abundance and species richness of Collembola, while specific root length was favorable to collembolan species richness. Wheat traits related to sensitivity to fungal diseases, (more especially septoria leaf blotch) and characteristics of aerial parts and roots impacted collembolan species and trait assemblages, but these effects were weak. Soil features, especially the proportion of coarse silt, were also influential. Our study did not show a favorable impact of wheat genetic diversity on soil Collembola, which might result from their low abundance. Nevertheless, it suggests correlations between some variety traits and the species richness and abundance of Collembola.
... Generalistic feeding is common among soil decomposers (Scheu, 2002), although there certainly are feeding preferences of faunal decomposers (Brückner et al., 2018). Particularly in deeper soil horizons, generalistic feeding allows utilization of a wider food range and, in turn, selection of resource-specific fatty acids (Endlweber et al., 2009). ...
Quantitative fatty acid signature analysis (QFASA) as a biochemical tool to study the diet composition of predators is frequently used in marine ecology to infer trophic links in vertebrate consumers. However, the potential and challenges of this method in other ecosystems have only recently been studied. The application in soil ecosystems leads to hurdles not encountered in the marine, such as the low similarity of fatty acid signatures between resource and consumer. So far, diet estimation attempts have been semisuccessful, necessitating to adapt QFASA for use in soil food webs. Dietary fat content may play an important role, as it influences consumer metabolism, and thus calibration coefficients for fatty acid trophic transfer. A series of feeding trials with baker's yeast spiked with five different pure fatty acids at various concentrations was conducted with Collembola, and the changes in calibration coefficients were observed. From there, equations were gained through regression analysis and new sets of calibration coefficients were calculated. QFASA was applied on a range of basal resources and the results compared with previously defined calibration coefficients. Calibration coefficients changed with the proportion of fatty acids in the diet and differed between the three Collembolan species. The re‐estimation of diets showed an improvement of model performance by the new calibration coefficients and indicated several modes of fatty acid assimilation. These greatly influence the outcome of diet estimation, for example, algal and bacterial diets are likely underestimated due to high metabolic turnover rates. The application of QFASA in soil ecosystems remains challenging. The variation in calibration coefficients and the resulting decrease in estimation deviation indicate the merit of calculating calibration coefficients from consumer signatures through linear or exponential equations. Ideally, the method should, when extended to the entire fatty acid signature, allow correct determination of consumer diets in soil food webs. The establishment of QFASA in soil food webs remains challenging due to low overlap in signature between resource and consumer and highly variable metabolic responses, impacting calibration coefficients. A series of experimental trials with baker's yeast spiked with five different pure fatty acids at various fat levels was conducted with Collembola, and the changes in calibration coefficients were observed. Calibration coefficients generally changed with the proportion of fatty acid in the diet and were markedly different between the three Collembolan species.
... Onychiuroidea are soil-adapted Collembola without eyes, pigment and furca (jumping organ). They are associated with plant roots, presumably by feeding on root tips or mycorrhizae (Endlweber et al., 2009;Fujii et al., 2016;. They have intermediate proportions of plant and fungal particles in their gut in comparison to other Collembola. ...
Trophic niche differentiation may explain coexistence and shape functional roles of species. In complex natural food webs, however, trophic niche parameters depicted by single and isolated methods may simplify the multidimensional nature of consumer trophic niches, which includes feeding processes such as food choice, ingestion, digestion, assimilation and retention.
Here we explore the correlation and complementarity of trophic niche parameters tackled by four complementary methodological approaches, that is, visual gut content, digestive enzyme, fatty acid and stable isotope analyses—each assessing one or few feeding processes, and demonstrate the power of method combination.
Focusing on soil ecosystems, where many omnivore species with cryptic feeding habits coexist, we chose Collembola as an example. We compiled 15 key trophic niche parameters for 125 species from 40 studies. We assessed correlations among trophic niche parameters and described variation of these parameters in different Collembola species, families and across life‐forms, which represent microhabitat specialisation.
Correlation between trophic niche parameters was weak in 45 out of 64 pairwise comparisons, pointing at complementarity of the four methods. Jointly, the results indicated that fungal‐ and plant‐feeding Collembola assimilate storage, rather than structural polysaccharides, and suggested bacterial feeding as a potential alternative feeding strategy. Gut content and fatty acid analyses suggested alignment between ingestion and assimilation/retention processes in fungal‐ and plant‐feeding Collembola. From the 15 trophic niche parameters, six were related to Collembola family identity, suggesting that not all trophic niche dimensions are phylogenetically structured. Only three parameters were related to the life‐forms, suggesting that species use various feeding strategies when living in the same microenvironments.
Consumers can meet their nutritional needs by varying their food choices, ingestion and digestion strategies, with the connection among different feeding processes being dependent on the consumed resource and consumer adaptations. Multiple methods reveal different dimensions, together drawing a comprehensive picture of the trophic niche. Future studies applying the multidimensional trophic niche approach will allow us to trace trophic complexity and reveal niche partitioning of omnivorous species and their functional roles, especially in cryptic environments such as soils, caves, deep ocean or benthic ecosystems.
... Considering that they live deeper in the soil profile, this group should be least sensitive to changes in plant coverage. However, of the springtail ecological groups eu-edaphic species may benefit most from root resources (Scheunemann et al., 2015) and have been shown to be able to switch to feeding on roots rather than soil organic matter resources when roots are in ample supply (Endlweber et al., 2009). In fact, van Eekeren et al., (2008) observed that compared to an annual crop rotation, the number of roots in autumn from 0 to 10 cm in a 3-year temporary grassland increased by Table 6 Mean values of soil suppressiveness associated variables by experimental treatment (n = 12) ± standard errors: final severity (0-4), infected plants (%), plant height-V. ...
The introduction of temporary grassland into an annual crop rotation is recognized to improve soil ecosystem services, and resulting legacies can be beneficial for the following crops. In this context, the aim of the present study was to evaluate legacy effects of introducing temporary grassland into an annual crop rotation on five ecosystem services (i) soil structure maintenance (aggregate stability), (ii) water regulation (saturated hydraulic conductivity), (iii) biodiversity conservation (microbial biomass and microbial metabolic activity, as well as microorganisms, enchytraeids, springtails and earthworm communities), (iv) pathogen regulation (soil suppressiveness to Verticillium dahliae), and (v) forage production and quality. Three crop rotation schemes, maintained for twelve years, were compared in four random blocks, one being an annual crop rotation without grassland (0 %), another with a medium percentage of grassland (50 %, corresponding to 3 years of continuous grassland in the crop rotation), and a third one with a high percentage of grassland in the crop rotation (75 %, corresponding to 6 years of continuous grassland in the crop rotation). The results showed that the grassland introduction into an annual crop rotation improved, whatever the duration of the grassland, soil structure maintenance and biodiversity conservation, while it decreased pathogen regulation and did not modify water regulation. Comparing the two crop rotations that included grassland, indicated a stronger beneficial grassland legacy effect for the higher proportion of grassland concerning soil structure maintenance and biodiversity conservation. By contrast, water regulation, pathogen regulation and forage production were not affected by the legacy of the 75 % grassland during the rotation. Overall, our findings demonstrated the extent to which grassland legacies are affecting the current state of soil properties and possible ecosystem services provided. To improve ecosystem services, soil management should take legacy effects into account and consider longer timeframes to apply beneficial practices.
... In turn, the abundance of euedaphic forms and the corresponding trophic group of springtails increased in this case, which may be explained not only by their habitation in deeper soil horizons [12] but also by their relative independence from colonization substrate [26]. It is considered that representatives of this group feed on mycorrhizal fungi [27], regulate the microbial community in the rhizosphere, and are involved in decomposition of soil organic matter [20]. Despite the change in the total abundance of springtails and the abundance of their individual trophic groups and life forms, their community structure does not vary between the plots (Fig. 1b), which is apparently explained by similarity of soil physicochemical properties. ...
The results are presented of studies on soil invertebrate communities (nematodes, springtails, and large invertebrates) in shore ecosystems near hydrogen sulfide springs in the valley of the Iska-Shor stream in the Adak reserve and along river valleys at the northern boundary of the taiga zone of the Komi Republic. The taxonomic richness of the studied invertebrate groups does not change between the sampling plots. The total abundance and the abundance of individual trophic groups of springtails and large soil invertebrates decrease in plant communities near the outlet of sulfide waters, but the structure of these groups remains similar between the plots. On the contrary, the structure of nematode complexes differs between the ecosystems of the river valleys and near the hydrogen sulfide springs, where the abundance of mycotrophs increases.
... All mesofauna detritivore taxa except Thysanoptera declined due to root trenching. Two pathways might have contributed to this reduction: reduced feeding on living roots and root hairs in particular by Diplura and some Collembola species (Gunn and Cherrett, 1993;Endlweber et al., 2009), or reduced feeding on fungi and bacteria associated with living roots in particular by Collembola, Oribatida and Protura (Fujii et al., 2016;Bluhm et al., 2019b). Indeed, root trenching in our study reduced vital fine roots by 50%, and also bacterial and fungal PLFA markers declined due to root trenching (Bluhm et al., 2019a). ...
Forest soil food webs have been assumed to be fueled substantially by root-derived resources. However, until today the flux of root-derived resources into soil animals has been investigated virtually exclusively using isotope labeling experiments, whereas studies on the consequences of disrupting the flux of root-derived resources into the soil animal food web are scarce. We here investigated the importance of root-derived resources for a wide range of soil animals by interrupting the resource flux into the soil of different forest types in Central Europe using a trenching experiment. We recorded the abundance of soil animal taxa varying in body size (micro-, meso-, and macrofauna) 1 and 3 years after root trenching, and quantified changes in biomass, species composition, and trophic shift using stable isotopes and NLFA analysis. Among the microfauna groups studied (trophic groups of Nematoda) only the abundance of plant feeding nematodes showed a trend in being decreased by-58% due to root trenching. Major soil mesofauna groups, including Collembola and Oribatida, suffered to a similar extent from root trenching with their abundance and biomass being reduced by about 30-40%. The soil macrofauna groups studied (Diplopoda, Isopoda, Chilopoda, Araneae, Coleoptera) generally were only little affected by root trenching suggesting that they rely less on root-derived resources than micro-and in particular mesofauna. Notably, the community structure of micro-, meso-, and macrofauna was not affected by root trenching. Further, we observed trophic shifts only in 2 out of 10 investigated species with the shifts generally being only minor. The results indicate that soil animal communities are markedly resilient to deprivation of root-derived resources suggesting that links to root-derived resources are non-specific. However, this resilience appears to vary with body size, with mesofauna including both decomposers as well as predators being more sensitive to the deprivation of root-derived resources than microfauna (except for root feeders) and macrofauna. Overall, this suggests that body size constrains the channeling of energy through soil food webs, with root-derived resources in temperate forests being channeled predominantly via soil taxa of intermediate size, i.e., mesofauna.
... Moreover, Collembola is more sensitive to climate warming than other groups, such as Acari, because of a thinner exoskeleton without a wax layer and greater water permeability of the cuticle (Convey et al., 2003). Collembola could also freely switch between detritus-derived (brown) to root-derived (green) food resources during different plant growth periods (Endlweber et al., 2009). Thus, Collembola is a suitable taxon that can be used for the evaluation of the simultaneous response to resource alterations and climate change by soil fauna. ...
Bottom-up or resource control is one of the most important aspects that determine the effects of climate change on soil fauna. It remains unclear whether the response of soil fauna to climate change is detritus-based or producer-based resource driven. Soil transplantation, from Heilongjiang to Jilin and Liaoning provinces, was used to simulate the effects of climate change on Collembola through different green or brown food resource treatments, which were represented by soybean cultivation (hereafter SC), land abandonment (LA), and vegetation removal (VR).
The results showed that soil southwestward transplantation to warmer region, Jilin and Liaoning, significantly increased density and biomass of Collembola in plant growth but not withered period. Structural equation modeling and redundancy analysis showed increasing food resources, such as plant biomass, microbial biomass, and soil organic carbon, during the warm or higher food-quality treatments directly increase the density and biomass of Collembola. Soil southwestward transplantation to warmer region, Jilin and Liaoning, significantly increase the density of Collembola in SC and LA. VR buffered the effect of soil transplantation on Collembola. It was concluded that the effects of soil transplantation on Collembola mainly occurred through the green but not brown food resource pathways.
... The nontarget soil fauna Collembola are one of the most ubiquitous soil fauna (Hopkin, 1997;Rusek, 1998;Bardgett and Putten, 2014). Collembola are commonly found in plant rhizospheres, and they are bound to be exposed to the Bt toxin in Bt crops field (Endlweber et al., 2009), so they can be used as indicators in evaluating the effects of Bt crops' cultivation on soil fauna (Arias-Martín et al., 2016;Song et al., 2019). Bt-506 is a Cry1Ac maize inbreed line that was independently developed by China Agricultural University. ...
The litters from Bt maize are always plowed into the soil after harvest. To clarify whether the decomposition rate of Bt litters and the nontarget soil fauna in the litters are influenced by Bt protein or the other organic matter, the leaf pieces of Bt-506, its near isoline Zheng 58 and a local type Zhengdan 958 were put into litterbags and buried into the field in Northeast China. Then, the Bt protein content of Bt-506 litters, the nonstructural carbohydrate and total nitrogen contents, and decomposition rates of all leaf litters and the collembolan communities in these litters were investigated after a period of buried time. There was 43.5 ng/g Bt protein remained in Bt-506 litters at the end of the experiment, when the Bt-506 litters had been kept in field for decomposition for 7 months. Except for Bt protein, none of the other investigated indexes were significantly different between Bt-506 and Zheng 58 at any sampling time. However, when compared with Zhengdan 958, the leaf litters of Bt-506 and Zheng 58 contained less nonstructural carbohydrate but more total nitrogen, and had lower decomposition rate, lower collembolan abundance and Shannon-Wiener index at some sampling times. Correlation analysis showed that the leaf litter decomposition rate and the collembolan abundance in litters were significantly correlated with the nonstructural carbohydrate content and the total nitrogen content of maize litters on May 20 (after buried in field for 6 months), and neither collembolan abundance nor leaf litter decomposition rate was correlated with maize type at any sampling time. In sum, Bt protein did not affect the decomposition rate of leaf litters and the collembolan community in litters; the differences of leaf litter decomposition rate and the collembolan community in litters between Bt-506, Zheng 58 and Zhengdan 958 were probably resulted from the different contents of nonstructural carbohydrate and total nitrogen in the leaf litters.
... Results found by Chamberlain, McNamara, Chaplow, Stott, and Black (2006) demonstrated that springtails are responsible for translocation of C in a vertical scale and changes in soil organic quality. In previous studies, for example, springtails affected soil C turnover mainly by affecting soil structure and microbial activity (Cragg & Bardgett, 2001;Endlweber, Ruess, & Scheu, 2009). ...
Tillage systems in conservation agriculture such as no‐tillage (NT) and crop‐livestock integration (CLI) have been proposed to limit the negative impacts of intensive agriculture. Soil organisms such as Collembola are good indicators because they respond to a variety of environmental and ecological factors and their community structure indicates a change in land management. In this study, we propose to assess the relationships between springtail biodiversity in management systems with a history of NT and CLI. For both management systems, nine points were sampled, distributed in a 30 × 30 m sampling grid, in three municipalities on the Southern Santa Catarina Plateau, Brazil. Springtails were collected using a metal cylinder (5 cm diameter × 5 cm deep) and identified at the species level. At the same point, samples were collected to evaluate soil properties (chemical, physical and microbiological). In total, 538 individuals were collected, distributed in 24 species, 293 individuals (18 species) in NT and 245 individuals (17 species) in the CLI system. Soil management systems studied did not affect the total number of individuals and richness. The NT system had a greater association with epigeic species, while the CLI system was more associated with hemiedaphic and edaphic species, which is related to the site‐specific differences in soil conditions. In both soil management systems, the species were influenced by a range of soil properties. The species Isotomurus sp. 1 and Lepidocyrtus sp. 1 were more influenced by soil properties in the NT system, while the species Proisotoma sp. 1, Sminthurinus sp. 1 and Tullbergia antarctica were more influenced by soil properties in the CLI system, compared to the others. Collembola community structure and species diversity were modified by the soil management systems. Our results suggest that the Collembola community may indicate changes across land management systems in conservation agriculture.
... Several studies have, though, employed stable isotope analysis to determine food sources of agrobiont invertebrates. Carbon isotopic analysis was applied to assess the contribution of weeds, maize and soil organic matter in the diet of soildwelling click beetle larvae , while 15 N/ 14 N ratio was used to detect a switch from detritivorous to herbivorous diet in a collembolan species in the presence of plants (Endlweber et al., 2009). The same ratio helped to reveal seasonal changes in the trophic levels of generalist predators (Birkhofer et al., 2011) and to demonstrate the impact of adding maize mulch on aboveground trophic cascades and pest control in wheat fields (Von Berg et al., 2010). ...
Food webs in agricultural systems are complex and trophic linkages are difficult to track using conventional methodologies. Here, we review three alternative approaches that allow empirical assessment of feeding interactions: DNA-based techniques, and stable isotope and fatty acid analyses. DNA-based methods, namely multiplex PCR and next-generation sequencing, allow identification of food types and host-parasitoid linkages, resulting in taxonomically highly resolved feeding networks. Stable isotopes and fatty acids reflect the assimilation of broader categories of resources, as metabolised into the consumers' tissue, together with the associated energy and nutrient fluxes in the food web. We discuss the strengths of the approaches but also highlight their limitations, providing practical advice on which technique is best suited to answer specific questions in examining food web interactions in agroecosystems. Future refinements of these techniques, especially when used in combination, could herald a new era in agricultural food web ecology, enabling management and environmental impact to be placed in the mechanistic context of trophic networks.
... In contrast, the concentration of 13 C changes little from diet to consumer, so it is a tracer of carbon sources used by the consumer (Peterson and Fry, 1987;Post, 2002). In Collembola, the δ 13 C value is closer to that of roots than that of litter, suggesting that the food supply of Collembola is derived from plants roots (Endlweber et al., 2009). The range of δ 15 N values is higher in euedaphic Collembola than in other life forms (Potapov et al., 2016), probably because euedaphic species consume a variety of food resources (Ponge, 2000). ...
The feeding ecology of soil animals is seldom investigated in the winter when the soil is covered with a layer of snow. Collembola (springtails) are winter-active arthropods that appear on the snow surface, especially on sunny days, and remain active in microhabitats under the snow. Since winter-active Collembola must be consuming food, we assessed the food resources for these Collembola with stable isotope and bacterial 16S rRNA gene amplicon sequencing methods. We collected two Desoria species from the snow surface and Tomocerus cf. jilinensis from subnivean microhabitats. The stable isotope signatures of winter-active Collembola species differed significantly from the soil litter layer. The isotopic signature of Desoria sp.1 was similar to the snow. Furthermore, the putative food resource (bacteria) ingested by Desoria sp.3 and Tomocerus cf. jilinensis were more from snow than from litter. All three Collembola species ingested a large proportion of Cyanobacteria. Moreover, a large proportion of bacteria associated with Collembola were putative symbionts. Bacterial communities and their associated metabolic functions were more similar in the two congeneric Desoria species than with Tomocerus cf. jilinensis. Our findings suggest that winter-active Collembola mainly feed on resources present in the snow layer. Stable isotope and amplicon sequencing methods are promising techniques to evaluate the diets of soil animals that remain active in snow-covered soils.
The underlying mechanisms of the relationships between tree species and the soil micro-food web in forest ecosystems remain uncertain, primarily ascribed to an insufficient understanding on how tree functional traits drive soil nematode communities, including in subtropical forests. We investigated the impacts of seven subtropical tree species (evergreen: Pinus massoniana, Mytilaria laosensis, Ilex chinensis, Michelia macclurei; and deciduous: Liquidambar formosana, Quercus acutissima, and Betula luminifera) on the soil nematode communities. We found that the abundance of soil nematodes was not affected by mycorrhizal types, but it was around 83% higher under the deciduous trees than the evergreen trees, indicating the importance of leaf phenology to the abundance of soil nematodes. Nonetheless, both the evergreen and the arbuscular mycorrhizal trees increased soil nematode diversity, resulting from changes in root traits and soil properties. Furthermore, root traits (root C, root N, and root C:N ratio), and soil properties (total C, total N, moisture content, and bulk density) were the best predictors of the community composition of soil nematodes, indicating a key role of resource quality and soil microhabitat in regulating soil nematodes. In contrast, the ectomycorrhizal trees had lower plant parasite and Wasilewska indices, and evenness, whereas the evergreen trees slightly improved the evenness of soil nematodes. This study suggests that tree species affect the soil food web through changes in soil conditions and plant functional traits in subtropical forests.
Belowground life relies on plant litter, while its linkage to living roots had long been understudied, and remains unknown in the tropics. Here, we analysed the response of 30 soil animal groups to root trenching and litter removal in rainforest and plantations in Sumatra, and found that roots are similarly important to soil fauna as litter. Trenching effects were stronger in soil than in litter, with an overall decrease in animal abundance in rainforest by 42% and in plantations by 30%. Litter removal little affected animals in soil, but decreased the total abundance by 60% in rainforest and rubber plantations but not in oil palm plantations. Litter and root effects on animal group abundances were explained by body size or vertical distribution. Our study quantifies principle carbon pathways in soil food webs under tropical land use, providing the basis for mechanistic modelling and ecosystem‐friendly management of tropical soils.
Some collembolan species can cause damage to greenhouse crops. This study investigates harmful effects of four different densities of springtails 0 (control), 20, 50, and 100 individuals at 22, 25, and 28 ˚C on germinating lettuce, radish, onion, and cucumber in laboratory (Petri dish) and semi-field pot experiments. Also, the effect of soil application of four pesticides (cypermethrin, fipronil, chlorpyrifos, and a biopesticide, matrine) was determined against collembolan individuals in cucumber and tomato greenhouses in Isfahan, Iran. The results of both laboratory and pot experiments showed that the collembolan species at low to high densities (20, 50, and 100 individuals per container) significantly reduced the seedling length and caused damage to lettuce, radish, onion, and cucumber plants at 22, 25, and 28 °C compared to that of control. In semi-field pot experiments, higher collembolan density (100 individuals per container) caused higher damage at low temperature treatment. Evaluation of soil applied pesticides in cucumber and tomato greenhouses showed that cypermethrin, fipronil, chlorpyrifos, and matrine significantly reduced population density of collembolan individuals compared to the control treatment. The results of this study demonstrated that the studied springtail species at various densities can cause damage to lettuce, radish, onion, and cucumber seedlings in greenhouses. The present study findings can be used in the integrated management of harmful springtails in the greenhouse crops.
In recent years, it has been increasingly recognized that soil animals are hidden reservoirs of antibiotic resistance genes (ARGs) and play a vital role in spreading ARGs in soil ecosystems. However, little is known about the variation of ARGs among different animals in the soil food web and effects of trophic levels and land uses on them. We characterized the antibiotic resistomes of 495 soil animal samples collected from six regions across China, including two different land uses. A total of 265 ARGs were detected in all animal samples, and relative abundances of ARGs in animals were significantly higher than in soils. In addition, significant differences in ARGs were observed among different animal groups. Twelve common ARGs were identified among all animal groups, accounting for 17.4% of total ARGs abundance. A positive and significant correlation was found between δ15N values (trophic level) and total ARGs abundance in animals. The relative abundance of ARGs in the soil food web from arable land was higher than forest land. Changes in soil antibiotics may indirectly affect animal resistome by altering soil ARGs. This study suggests that the risk of ARGs spreading through the food web is greater in arable than in forest ecosystems.
Soil collembolans live in close proximity to plant roots and may have a role in the phytoextraction of potentially toxic metals from contaminated soils but the underlying mechanisms remain poorly investigated. We hypothesize that soil collembolans may change the root morphology of hyperaccumulators by regulating plant physiological characteristics. Here, a pot experiment was conducted in which a cadmium (Cd) and zinc (Zn) hyperaccumulator (Sedum plumbizincicola) was grown with or without a collembolan (Folsomia candida), and plant transcriptome and hormones as well as the root characteristics of S. plumbizincicola were analyzed. F. candida promoted the growth and Cd/Zn uptake of S. plumbizincicola, the root and shoot biomass increasing by 53.3 and 34.4%, and the uptake of Cd and Zn in roots increased by 83.2 and 65.4%, respectively. Plant root morphology, total root length, root tip number and lateral root number increased significantly by 40.7, 37.2 and 33.8%, respectively, with the addition of F. candida. Transcriptome analysis reveals that the expression levels of defense-related genes in S. plumbizincicola were significantly up-regulated. In addition, the defensive plant hormones, i.e. salicylic acid in the roots, increased significantly by 338%. These results suggest that the plant in defense of the action of F. candida regulated the expression of the corresponding genes and increased the defensive plant hormones, thus modifying root morphology and plant performance. Overall, this study highlights the importance of the regulation by collembolans of plant growth and metal uptake by interaction with hyperaccumulator roots.
The dynamics of C in terrestrial ecosystems can be traced on the basis of the marked differences in the δ¹³C signatures of plants possessing the C3, C4 or CAM photosynthetic pathways. When two C sources differing in natural ¹³C abundance (δ¹³C) contribute to a mixture, the relative contribution of each can be quantitatively apportioned by the use of a two-end-member mixing model. This ability of δ¹³C to partition source is unique among stable isotopes important in the biosphere, where with few exceptions, natural abundance signatures are used as qualitative rather than quantitative tracers because of isotopic fractionation. The many and varied applications of δ¹³C in apportioning C source are examined herein. They include estimation of soil organic matter turnover due to either a known or presumed change in vegetation cover, the contribution of organic materials to the soil C pool, the contribution of C source to vertebrate and invertebrate diets, disentangling roots in mixed C3–C4 stands, and partitioning the sources of respired CO2 in various C3–C4 mixtures, i.e., between plants and soil, between plants, between animal excreta slurries and soil, within fungal media and within biochar-amended soil.
The Songnen Plain of China was once an important grassland used for sheep grazing, but it has largely been degraded to bare saline-alkaline land (BSAL). BSAL consists of plant-free areas characterized by high soil pH values (up to 10) and salt and alkali (e.g., Na+ and Ca2+) contents, as well as low soil organic matter and water contents; thus, very few soil faunal species can survive on BSAL. The recovery of degraded ecosystems provides a great opportunity to investigate the reconstruction of belowground soil faunal communities. Collembola are a class of widespread and abundant soil fauna that can colonize this harsh environment. Habitat changes on BSAL promote aboveground revegetation, which greatly facilitates the recovery of Collembola. A soil transfer experiment on the BSAL of the Songnen Plain was conducted to study the effects of habitat and Collembola morphological traits on the recovery process of Collembola. Defaunated and with-fauna soil blocks were transferred among three habitats: BSAL, reclaimed arable land, and naturally revegetated grassland. The recovered Collembola in the transferred soil blocks were compared two, seven, and twelve weeks after the start of the experiment. The results showed that (1) the majority of the Collembola, regardless of their morphological traits, recovered in the defaunated soil blocks within two weeks; (2) generalists and habitat-preferring species recovered faster than specialists; (3) the average total abundance, species richness, and community composition of Collembola recovered to the natural levels in two weeks; and (4) twelve weeks after replacement, the highest average total abundance and species richness of Collembola were found in the arable land. Our results indicate that the majority of Collembola in this study, regardless of their dispersal type, which is related to their morphological traits, are fast dispersers, and their recovery speeds are mainly affected by habitat preferences. We suggest that the reclamation of BSAL to arable land rather than its natural recovery to grassland aids in the recovery of Collembola in degraded grassland systems.
The trophic niche of an organism is tightly related to its role in the ecosystem and to interactions with other species. Thousands of species of soil animals feed on detritus and co-exist with apparently low specialisation in food resource use. Trophic niche differentiation may explain species coexistence in such a cryptic environment. However, most of the existing studies provide only few and isolated evidence on food resources, thus simplifying the multidimensional nature of the trophic niches available in soil.
Focusing on one of the most diverse soil taxa – springtails (Collembola) – we aimed to reveal the additional value of information provided by four complementary methods: visual gut content-, digestive enzyme-, fatty acid- and stable isotope analyses, and to demonstrate the multidimensional nature of trophic niches.
From 40 studies, we compiled fifteen key trophic niche parameters for 125 species, each analysed with at least one method. Focusing on interspecific variability, we explored correlations of trophic niche parameters and described variation of these parameters in different Collembola species, taxonomic groups and life forms.
Correlation between trophic niche parameters of different methods was weak in 45 out of 64 pairwise comparisons, reflecting the complementarity of the multidimensional trophic niche approach. Gut content and fatty acids provided comparable information on fungivory and plant feeding in Collembola. Information provided by digestive enzymes differed from that gained by the other methods, suggesting its high additional value. Stable isotopes were mainly related to plant versus microbial feeding. Many parameters were affected by taxonomic affiliation but not life form. Furthermore, we showed evidence of bacterial feeding, which may be more common in Collembola than usually assumed.
Different methods reveal different feeding dimensions, together drawing a comprehensive picture of the trophic niche in taxa with diverse feeding habits. Food web studies will benefit from simultaneously applying several joint approaches, allowing to trace trophic complexity. Future studies on the multidimensional trophic niche may improve understanding of food-web functioning and help to explain species coexistence in cryptic environments such as soil.
Soil organic matter (SOM) and pH are key ecosystem drivers, influencing resilience to environmental change. We tested the separate effects of pH and SOM on nutrient availability, plant strategies, and soil community composition in calcareous and acidic Grey dunes (H2130) with low, intermediate, and/or high SOM, which differ in sensitivity to high atmospheric N deposition. Soil organic matter was mainly important for biomass parameters of plants, microbes, and soil animals, and for microarthropod diversity and network complexity. However, differences in pH led to fundamental differences in P availability and plant strategies, which overruled the normal soil community patterns, and influenced resilience to N deposition. In calcareous dunes with low grass‐encroachment, P availability was low despite high amounts of inorganic P, due to low solubility of calcium phosphates and strong P sorption to Fe oxides at high pH. Calcareous dunes were dominated by low‐competitive arbuscular mycorrhizal (AM) plants, which profit from mycorrhiza especially at low P. In acidic dunes with high grass‐encroachment, P availability increased as calcium phosphates dissolved and P sorption weakened with the shift from Fe oxides to Fe‐OM complexes. Weakly sorbed and colloidal P increased, and at least part of the sorbed P was organic. Acidic dunes were dominated by nonmycorrhizal (NM) plants, which increase P uptake through exudation of carboxylates and phosphatase enzymes, which release weakly sorbed P, and disintegrate labile organic P. The shifts in P availability and plant strategies also changed the soil community. Contrary to expectations, the bacterial pathway was more important in acidic than in calcareous dunes, possibly due to exudation of carboxylates and phosphatases by NM plants, which serve as bacterial food resource. Also, the fungal AM pathway was enhanced in calcareous dunes, and fungal feeders more abundant, due to the presence of AM fungi. The changes in soil communities in turn reduced expected differences in N cycling between calcareous and acidic dunes. Our results show that SOM and pH are important, but separate ecosystem drivers in Grey dunes. Differences in resilience to N deposition are mainly due to pH effects on P availability and plant strategies, which in turn overruled soil community patterns.
In soil a high number of species co-exist without extensive niche differentiation, which was assigned as ‘the enigma of soil animal species diversity’. In particular, the detritivores are regarded as food generalists. We have investigated nitrogen stable isotope ratios (15N/14N) of a major decomposer group, the Collembola, to evaluate trophic relationship and determine feeding guilds. Additionally, the δ15N values of potential food sources such as mosses, lichens and other plant derived material (bark, nuts, leaves) were analysed. The natural variation in nitrogen isotopes was assessed in 20 Collembola taxa from three deciduous forest stands. The δ15N signature formed a continuum from phycophages/herbivores to primary and secondary decomposers, reflecting a gradual shift from more detrital to more microbial diets. The δ15N gradient spanned over 9 δ units, which implies a wide range in food sources used. Assuming a shift in 15N of about 3 ‰ per trophic level, the results indicate a range of three trophic levels. These variations in 15N/14N ratios suggest that trophic niches of Collembola species differ and this likely contributes to Collembola species diversity.
An on-line method for the determination of N and C with a gas isotope mass spectrometer (Finnigan, MAT 251) was developed to improve the sensitivity and to reduce measurements time and the cost of the sample analysis. For this purpose an elemental analyser (Carlo Erba, NA 1500) was coupled to the mass spectrometer using parts of the capillary system of a trapping box (Finnigan, type CN). For the determination of samples with natural concentrations of N and C the uncertainty of the delta value is less than 0.2 δ‰. The detection limit is in the order of 10 μg (total N or total C) and 7 samples can be analysed per hour.
To obtain nutrients mineralised from organic matter in the soil, plants have to respond to its heterogeneous distribution. We measured the timing of nitrogen uptake by wheat from a localised, 15N labelled organic residue in soil, as well as the timing of changes in root length density. We calculated the rates of N uptake per unit root length (inflows) for roots growing through the residue and for the whole root system. A stimulated local inflow appeared to be the main mechanism of exploitation of the residue N during the first five days of exploitation. 8% of the N that the plants would ultimately obtain from the residue was captured in this period. Roots then proliferated in the residue. This, together with a rapidly declining N inflow, contributed to the capture, over the next seven days, of 63% of the N that the plants derived from the residue. After that time, massive root proliferation occurred in the residue, but relatively little further N was captured.
Effects of Collembola (Heteromurus nitidus and Onychiurus scotarius) and earthworms (Aporrectodea caliginosa and Octolasion tyrtaeum) on the growth of two plant species from different functional groups (Poa annua and Trifolium repens), and on the development of aphids (Myzus persicae) were investigated in a laboratory experiment lasting 20 weeks. Using soil from a fallow site which had been set aside for
about 15 years, we expected that nitrogen would be of limited supply to plants and hypothesized that the soil animals studied,
particularly earthworms, would increase nutrient availability to plants and thereby also modify aphid reproduction and development.
Plant growth was modified strongly by the presence of soil animals. Earthworms caused a more than twofold increase in shoot
and root mass of P. annua but increased that of T. repens by only 18% and 6%, respectively. However, earthworms neither affected plant shoot/root ratio nor the nitrogen concentration
in plant tissue. In contrast, the presence of Collembola caused a reduction in plant biomass particularly that of P. annua roots, but plant tissue nitrogen concentration was increased, although only slightly. Aphid reproduction on T. repens was lowered in the presence of Collembola on average by 45% but on P. annua increased by a factor of about 3. It is concluded that Collembola decrease aphid reproduction on more palatable host plants
like T. repens but increase that on less palatable ones like P. annua. Earthworm presence also affected aphid reproduction but the effect was less consistent than that of Collembola. In the presence
of earthworms, aphid reproduction was in one experimental period increased by some 70%. Earthworms also modified the numbers
of Collembola and their vertical distribution in experimental chambers. Exploitation of deeper soil layers by H. nitidus was increased but, generally, O. scotarius numbers were reduced whereas those of H. nitidus increased in earthworm treatments. The presence of Collembola also influenced earthworm body mass during the experiment.
In general it declined, but in the presence of Collembola loss of body mass of A. caliginosa was more pronounced. We conclude that inhibiting effects between Collembola and earthworms resulted from the use of a common
resource, litter material rich in nitrogen. This is supported by the higher C/N ratio of the litter material in the presence
of earthworms and Collembola by the end of the experiment. Effects of soil invertebrates like Collembola and earthworms on
plant performance and aphid development are assumed to be modified by complex direct and indirect interactions among soil
animal groups.
Mycorrhizal fungi influence plant nutrition and therefore likely modify competition between plants. By affecting mycorrhiza
formation and nutrient availability of plants, Collembola may influence competitive interactions of plant roots. We investigated
the effect of Collembola (Protaphorura fimata Gisin), a mycorrhizal fungus (Glomus intraradices Schenck and Smith), and their interaction on plant growth and root structure of two plant species, Lolium perenne L. (perennial ryegrass) and Trifolium repens L. (white clover). In a laboratory experiment, two individuals of each plant species were grown either in monoculture or
in competition to the respective other plant species. Overall, L. perenne built up more biomass than T. repens. The clover competed poorly with grass, whereas the L. perenne grew less in presence of conspecifics. In particular, presence of conspecifics in the grass and presence of grass in clover
reduced shoot and root biomass, root length, number of root tips, and root volume. Collembola reduced shoot biomass in L. perenne, enhanced root length and number of root tips, but reduced root diameter and volume. The effects of Collembola on T. repens were less pronounced, but Collembola enhanced root length and number of root tips. In contrast to our hypothesis, changes
in plant biomass and root structure in the presence of Collembola were not associated with a reduction in mycorrhizal formation.
Presumably, Collembola affected root structure via changes in the amount of nutrients available and their spatial distribution.
The stable isotopes of nitrogen (d15N) and carbon (d13C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how d 15N and d13C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of d15N is 3.4‰ (1 SD 5 1‰) and of d13 Ci s 0.4‰ (1 SD 5 1.3‰), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of d15N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of d13C when d13C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions
Decomposer invertebrates influence soil structure and nutrient mineralization as well as the activity and composition of the microbial community in soil and therefore likely affect plant performance and plant competition. We established model grassland communities in a greenhouse to study the interrelationship between two different functional groups of decomposer invertebrates, Lumbricidae and Collembola, and their effect on plant performance and plant nitrogen uptake in a plant diversity gradient. Common plant species of Central European Arrhenatherion grasslands were transplanted into microcosms with numbers of plant species varying from one to eight and plant functional groups varying from one to four. Separate and combined treatments with earthworms and collembolans were set up. Microcosms contained 15N labeled litter to track N fluxes into plant shoots. Presence of decomposers strongly increased total plant and plant shoot biomass. Root biomass decreased in the presence of collembolans and even more in the presence of earthworms. However, it increased when both animal groups were present. Also, presence of decomposers increased total N concentration and 15N enrichment of grasses, legumes, and small herbs. Small herbs were at a maximum in the combined treatment with earthworms and collembolans. The impact of earthworms and collembolans on plant performance strongly varied with plant functional group identity and plant species diversity and was modified when both decomposers were present. Both decomposer groups generally increased aboveground plant productivity through effects on litter decomposition and nutrient mineralization leading to an increased plant nutrient acquisition. The non-uniform effects of earthworms and collembolans suggest that functional diversity of soil decomposer animals matters and that the interactions between soil animal functional groups affect the structure of plant communities.
Microorganisms have a variety of evolutionary adaptations and physiological acclimation mechanisms that allow them to survive and remain active in the face of environmental stress. Physiological responses to stress have costs at the organismal level that can result in altered ecosystem-level C, energy, and nutrient flows. These large-scale impacts result from direct effects on active microbes' physiology and by controlling the composition of the active microbial community. We first consider some general aspects of how microbes experience environmental stresses and how they respond to them. We then discuss the impacts of two important ecosystem-level stressors, drought and freezing, on microbial physiology and community composition. Even when microbial community response to stress is limited, the physiological costs imposed on soil microbes are large enough that they may cause large shifts in the allocation and fate of C and N. For example, for microbes to synthesize the osmolytes they need to survive a single drought episode they may consume up to 5% of total annual net primary production in grassland ecosystems, while acclimating to freezing conditions switches Arctic tundra soils from immobilizing N during the growing season to mineralizing it during the winter. We suggest that more effectively integrating microbial ecology into ecosystem ecology will require a more complete integration of microbial physiological ecology, population biology, and process ecology.
Fungal feeding soil invertebrates feed on a wide spectrum of fungal species suggesting that mixed diets increase fitness. We investigated relationships between food preferences for seven saprophytic fungal species/forms and fitness parameters (mortality, growth, time to reproduction, reproduction, egg size) in two Collembola species, Folsomia candida and Protaphorura armata. The fungal species/forms studied included the wild type and a melanin-deficient form of Aspergillus fumigatus to investigate the role of melanin in collembolan nutrition. Also, three mixed diets consisting of a preferred fungal species (Cladosporium cladosporioides) and species of intermediate or low food quality were investigated. Both Collembola species preferred similar fungal species/forms as food. Food preference generally matched fitness parameters, i.e. growth and reproduction of Collembola was at a maximum when feeding on preferred fungi. This was not the case for A. fumigatus. The wild type and the melanin-deficient form ranked among the least preferred fungi. Growth and reproduction of Collembola were low when feeding on the wild type but high when feeding on the melanin-deficient form indicating that the Collembola misjudged the food quality of the latter in the preference tests. The results show for the first time that genes driving melanin syntheses (pksP) strongly affect the food quality of fungi for fungal feeding invertebrates. Feeding on mixed diets generally increased growth and reproduction of Collembola except when the diets included toxic species (Penicillium sp.). The results support the nutrient balance hypothesis and also show that the detection of toxic species in the diet is important. They indicate that the widespread generalist feeding mode of Collembola maximizes fitness if toxic fungal species are avoided. The fitness parameters growth, reproduction and time until onset of reproduction were correlated closely but egg volume, which also varied with fungal diet, correlated poorly with the other fitness parameters. Variation in egg size with fungal diet shows that the diet of Collembola may have transgenerational effects.
This chapter provides an overview of the mechanisms of microarthropod by focusing on the microbial interactions in soil. Microarthropods control the distribution and abundance of fungi in soil, and they stimulate microbial metabolic activity, thereby amplifying microbial immobilization or mineralization of nutrients. Microarthropods are important as vectors of entomopathogenic fungi to holometabolous insects. In soils where fungi dominate, there are six mechanisms of interaction with microarthropods. Two control fungal distribution and abundance––namely, selective grazing of fungi by microarthropods and dispersal of fungal inoculum by microarthropods. Four additional mechanisms stimulate microbial activity: (1) direct supply of mineral nutrients in urine and feces, (2) stimulation of bacterial activity by microarthropod activity, (3) compensatory fungal growth due to periodic microarthropod grazing, and (4) release of fungi from competitive stasis due to microarthropod disruption of competing mycelial networks. Microarthropods carry fungal propagules, including those of root pathogens, to root surfaces. They also graze fungi on root surfaces, and selectively consume saprophytic fungi. In the rhizosphere, the mechanisms of interaction are dispersal and selective grazing. Simulation models of soil food webs might include responses to microarthropods.
Naturally occurring stable isotopes of carbon and nitrogen are powerful tools to investigate food webs, where the ratio of 15N/14N is used to assign trophic levels and of 13C/12C to determine the food source. A shift in δ15N value of 3‰ is generally suggested as mean difference between two trophic levels, whereas the carbon isotope composition of a consumer is assumed to reflect the signal of its diet. This study investigates the effects of food quality, starvation and life stage on the stable isotope fractionation in fungal feeding Collembola. The fractionation of nitrogen was strongly affected by food quality, i.e. the C/N ratio of the fungal diet. Collembola showed enrichment in the heavier isotope with increasing N concentration of the food source. Δ15N varied between 2.4‰, which assigns a shift in one trophic level, and 6.3‰, suggesting a shift in two trophic levels. Starvation up to 4 weeks resulted in an increase in the total δ15N value from 2.8‰ to 4.0‰. Different life stages significantly affected the isotope discrimination by Collembola with juveniles showing a stronger enrichment (Δ15N=4.9‰) compared to adults (Δ15N=3.5‰). Δ13C varied between −2.1‰ and −3.3‰ depending on the food quality, mainly due to compensational feeding on low quality diet. During starvation δ13C value decreased by 1.1‰, whereas the life stage of Collembola had no significant effect on isotopic ratios. The results indicate that the food resource and the physiological status of the consumer have important impact on stable isotope discrimination. They may cause differences in fractionation rate comparable to trophic level shifts, a fact to consider when analysing food web structure.
The article reviews recent publications dealing with relationships between Collembola, carbon and nitrogen turnover. Under field conditions, correlations between Collembola, total C and N are usually weak. More pronounced interdependences can be found with microbial parameters, especially when using multivariate statistics and sampling at high temporal resolution. Many manipulation experiments have revealed strong and usually positive impacts of Collembola on N mineralisation, soil respiration, leaching of dissolved organic carbon and plant growth. The effects are mostly indirect and depend on temperature, water content, substrate quality, population density, Collembola species, plant species and in particular on interactions with other soil biota. Key mechanisms are fungal feeding, distribution of fungal propagules, root herbivory and predation on nematodes. Omnivory is probably the prevailing feeding strategy in Collembola. Finally, a tentative conceptual model for arable soils is given, explaining the differing effects of Collembola on C and N turnover by switching feeding strategies according to environmental conditions.
A food web presented for soil meso- and macroinvertebrates in grassland has many characteristics (eg number of trophic links, frequency distribution of food chain lengths, linkage density, connectance) in common with webs of similar size from other habitats but there are also important differences. There are unusually low proportions of trophic links between top and intermediate species. The proportion of links with basal species is very high. There was a high degree of omnivory, no clear compartmentation, and separate herbivore and decomposer food webs could not be distinguished. Plant root systems were an important resource for many soil animals. There was no clear evidence for exclusive guilds or species packing. -from Authors
1. In the laboratory, a microcosm experiment was set up to study (1) the interaction between two collembolan species Onychiurus furcifer (Börner) and Heteromurus nitidus (Templeton) during 24 weeks of incubation; (2) the influence of slug (Arion rufus L.) cast material on the outcome of this interaction; and (3) the influence of collembolan activity on microbial biomass, respiration and nutrient mobilization.
2. The CO2 production was monitored every other week and NH4+, NO3– and PO43– contents of leachates were determined every 4 weeks. After 12 and 24 weeks of incubation, the number of collembolans, basal respiration (O2 consumption), microbial biomass (substrate-induced respiration method), specific respiration (qO2) and the content of NH4+, NO3– and PO43– in soil were determined.
3. Generally, the number of collembolans in microcosms with cast material exceeded that of microcosms without cast material considerably on average by factors of 20 and 26 for O. furcifer and H. nitidus, respectively. This increase was attributed to the additional food supply provided with the cast material. Numbers of collembolans declined during the experiment.
4. At both sampling dates, the presence of H. nitidus led to a reduction in the number of O. furcifer, whereas H. nitidus benefited from the presence of O. furcifer. Either trophic or non-trophic mechanisms, or both, may have caused this interaction (contramensalism, sensuArthur & Mitchell 1989).
5. Both collembola species caused a decrease in microbial respiration, decomposition rates and tentatively also microbial biomass at high densities, whereas at low densities microbial respiration was stimulated while decomposition rates and microbial biomass remained unaffected. These effects were more pronounced for O. furcifer than for H. nitidus.
6. In treatments with cast material N-mobilization was increased by collembolan activity.
Reproduction of Heteromurus nitidus (Collembola) feeding on conidial fungi, ectomycorrhizal fungi and soil algae in single and mixed diets was investigated. Feeding on mixed diets generally increased Collembola reproduction even in combinations of fungi/algae of high food quality with those of low food quality, indicating that Collembola generally benefit from feeding on mixed diets.
The contribution of dietary species in mixed diets to Collembola nutrition was quantified using stable isotope methods. Incorporation of carbon from fungal/algal species into H. nitidus in mixed diets varied with food quality indicating that Collembola are able to adjust the proportion of food materials ingested to maximize fitness.
Fractionation of ¹³ C and ¹⁵ N in H. nitidus feeding on single and mixed diets varied between diets and differed between juveniles and adults. The trophic structure of fungal feeding soil invertebrates cannot be inferred in a straightforward way from variations in natural abundances of stable isotopes, rather, stable isotope signatures reflect feeding guilds.
Decomposer animals stimulate plant growth by indirect effects such as increasing nutrient availability or by modifying microbial communities in the rhizosphere. In grasslands, the spatial distribution of organic matter (OM) rich in nutrients depends on agricultural practice and the bioturbation activities of large detritivores, such as earthworms. We hypothesized that plants of different functional groups with contrasting nutrient uptake and resource allocation strategies differentially benefit from sites in soil with OM accumulation and the presence of decomposer animals. In a greenhouse experiment we investigated effects of spatial distribution of 15N-labelled grass litter, earthworms and collembola on a simple grassland community consisting of Lolium perenne (grass) and Trifolium repens (legume). Litter aggregates (compared to homogeneous litter distribution) increased total shoot biomass, root biomass and 15N uptake by the plants. Earthworms and collembola did not affect total N uptake of T. repens; however, the presence of both increased 15N uptake by T. repens and L. perenne. Earthworms increased shoot biomass of T. repens 1.11-fold and that of L. perenne 2.50 fold. Biomass of L. perenne was at a maximum in the presence of earthworms, collembola and with litter concentrated in a single aggregate. Shoot biomass of T. repens increased in the presence of collembola, with L. perenne generally responding opposingly. The results indicate that the composition of the decomposer community and the distribution of OM in soil affect plant competition and therefore plant community composition.
We studied the effects of varied collembolan numbers on three compensatory mechanisms of nutrient uptake: fine root mass, endomycorrhizal development, and physiological uptake capacity. We grew ash (Fraxinus pennsylvanica) with or without the arbuscular mycorrhizal fungus Glomusintraradices, with 0, 10 or 50 initial Collembola (Folsomia candida). After 83 d root and uptake rates, endomycorrhizal development, and plant biomass were determined. Plant mass increased with Collembola number. Collembola interacted with mycorrhizae in their effects on N uptake and leaf N. Collembola in the absence of mycorrhizal roots were associated with lower N uptake and leaf N at 10 than at 0 or 50 initial Collembola. In contrast, Collembola in the presence of mycorrhizal roots were associated with the highest rate of N uptake and leaf N at 10 versus 0 or 50 initial Collembola. Hence as initial Collembola number increased, the relative importance of root system traits that determined N uptake changed from root physiological uptake capacity, presence of mycorrhizal roots, to fine root biomass.
We investigated whether the capacities of Lolium perenne L. and Poa pratensis L. roots to proliferate locally and to alter local nitrogen (N) inflows in a decomposing organic matter patch were important in their capture of N when grown together. In the presence of a patch, plants of both species were significantly heavier and contained more N. Root length and weight densities increased in the patch, but specific root length was unaltered. Although both species proliferated roots in the patch, L. perenne produced greater root length densities than P. pratensis, and also captured more N from the patch. Indeed, total N uptake from the patch was related to root length density within the patch. N inflows (rate of N uptake per unit root length) in the patch were no faster than in the whole root system for both species. Under the conditions of this study, root proliferation in an organic patch was more important for N capture from the patch than alterations in N inflows. Local proliferation of roots may be a key factor in interspecific competition for non-uniformly distributed supplies of N in natural habitats, so resolving the previous uncertainty as to the ‘adaptive’ nature of root proliferation.
1 We used Lolium perenne plants grown in microcosms to investigate the responses of root demography, plant N capture, soil fauna populations and microbial community profiles to five organic patches containing the same amount of N but differing in their chemical and physical complexity and C : N ratio. All patches were dual labelled with 15N/13C. Control patches contained the background sand : soil mix only.
2 There was rapid decomposition in, and plant N capture from, the patches of lowest C : N ratio. Early in the experiment 13C was detected in the soil atmosphere and 15N in the shoots. No 13C enrichment was detected in the plant material.
3 The rate of root production was slowest in the most complex patch (L. perenne shoot material) but accelerated when patches were simpler and had lower C : N ratios. There was no difference in root mortality between treatments.
4 Nitrogen concentrations of shoots and roots and shoot biomass were greater in the N-containing patches than controls, except for the most complex patch, while root biomass did not differ with treatments.
5 Total plant N capture was 45–54% of that initially added in patches that had a C : N ratio < 4. However, in the most complex patch (C : N ratio c. 21 : 1) plants captured only 11% of the N added.
6 Biomass of microbial-feeding protozoa was related to soil NO3–-N concentration in the patch but not to numbers of microbial-feeding nematodes. Patches of greater complexity increased the metabolic diversity of the microbial community (i.e. the number of substrates used in a Biolog GN plate) and altered the pattern of substrate utilization.
7 At harvest, the amount of patch-derived N estimated to be in the microbial biomass was much smaller (i.e. 7–13%) than in the plant tissues. Thus, plants were highly effective competitors with micro-organisms when capturing N supplied in patches with a low C : N ratio.
Laboratory microcosms containing litter from three tussock grasslands were used to assess the impact of grazing by a collembolan, Onychiurus procampatus, on the abundance, nutrient release, and respiration of the saprotrophic fungus, Phoma exigua. The fungal biomass and respiration rate were significantly reduced only when Collembola were present in excess of mean field densities but perhaps more typical of spatial aggregations in the soil. A high efficiency of nutrient immobilization by P. exigua was demonstrated but nutrient release was not significantly affected by the fauna. Problems associated with the use of microcosms in the simulation of field conditions are discussed.
The functional roles of the fungivorous collembolan Tomocerus minor and the detritivorous isopod Philoscia muscorum during the decomposition of Pinus nigra needles were studied in mesocosms filled with two different types of F1 litter, obtained from two different forest soils. The effects of the animals on the availability of K+, Ca2+, NO
inf3
sup-
, NH
inf4
sup+
, and PO
inf4
sup3-
and on the respiration, dehydrogenase, and cellulase activity of microorganisms were measured over one growing season. The animals were introduced into the F1 litter in three densities. The most important animal effect was a buffering effect, in that addition of the animals increased nutrient availability and microbial activity where the corresponding values in control mesocosms without animals were low, and decreased the nutrient availability and microbial activity where control values were high. This effect occurred for both species and was most evident in the substrate with the highest temporal fluctuations. The effects on nutrient availability are attributed to an animal effect on the activity of and successional stage reached the microbial community, with NH
inf4
sup+
availability seen as the most important factor. The concept of functional groups in relation to these animal effects is discussed.
Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.
This microcosm study is concerned with understanding those factors which regulate ecosystem processes of nutrient cycling and plant productivity in a montane grassland ecosystem. We examined the effects of different groups of soil fauna, namely bacterial-feeding nematodes and Collembola, on nutrient mineralization (N and P) in an acid, organic soil taken from a montane grassland in the Peak District National Park, United Kingdom. We also examined whether faunal influences on nutrient release, a measure of nutrient mineralization, resulted in changes in nutrient uptake and biomass production of an indigenous montane grass species (Nardus stricta (L.)). We found that in the presence of Collembola, and when nematodes and Collembola were combined, N mineralization, nutrient leaching and shoot N contents of N. stricta was significantly increased relative to a defaunated control. We also found that net P mineralization and leaching increased (although not significantly) in the presence of both nematodes and Collembola, resulting in a significant increase in shoot P content of N. stricta. The presence of nematodes alone, which were largely bacterial-feeders, had no effect on the mineralization of N or P, or shoot nutrient content. We suggest that differences in the effect of faunal treatments on nutrient mineralization are related to the feeding strategies of the added fauna, and to their consequent effect on the size of the soil microbial biomass. The treatments that increased N mineralization and plant nutrient content (N and P) also significantly reduced plant growth (shoot and root). We suggest that high NH4+–N concentrations in the soil solution of Collembola treatments inhibited the growth of N. stricta and that the growth of other grassland species may benefit from this improvement in nutrient availability.
Fungal feeding decomposer animals in soil appear to prefer dark pigmented microfungi (often termed Dematiacea) when given the choice. Both fruiting species (e.g. Cladosporium, Alternaria, Ulocladium) and species with sterile dark mycelia are preferred to hyaline species. In laboratory feeding choice experiments other fungi than dark pigmented forms were less preferred (e.g. Trichoderma, Fusarium, and Zygomycetes like Mucor and Mortierella) or rejected even when there was no other choice (e.g. Penicillium, Aspergillus). Interestingly, the soil mesofauna seems to be more selective than the soil macrofauna. These findings are in contrast to the assumption that decomposer animals and soil fungi co-evolved in a way similar to plants and pollinating animals above the ground. The lack of co-evolution between decomposer animals and soil fungi is surprising since below-ground systems are much older than above-ground systems, and therefore, there was more time for co-evolutionary processes. Furthermore, the findings contradict the explanation of the high diversity of fungal feeding decomposer animals by partitioning of food resources. In general, fungal feeding decomposer animals appear to be food generalists rather than specialists. Dark pigmented fungi often comprise 30-60% of fungal isolates from soils; virtually all of them appear to be of high food quality. Four reasons may explain the preference of fungal feeding decomposer animals for dark pigmented fungi. (1) Dark pigmented fungi contain more carbon or nutrients than other fungi. This, however, is unlikely because melanins, the characteristic components of dark pigmented fungi, are recalcitrant compounds, which are hard to digest. (2) Dark pigmented fungi may produce more efficient exo-enzymes than other fungi thereby effectively digesting organic compounds, which may serve as food for the decomposer animals. In this case, the attempt of decomposer animals to feed on dark pigmented fungi only reflects that the animals seek to exploit the superior enzymatic capabilities of dark pigmented fungi (‘external rumen hypothesis’). (3) Dark pigmented fungi may be used as indicators of organic material, which is at a specific stage of decomposition, and therefore, contains nutrients in high concentrations. (4) Dark pigmented fungi may be preferred because they are less toxic than other fungi, or decomposer animals avoid chitinolytic fungi like Trichoderma, Penicillium, Paecilomyces and Mortierella because the animals are in danger of being digested by these fungi. Each of the four hypotheses is little supported by experimental proof and this review, therefore, calls for a more detailed experimental analysis of decomposer animal-soil fungal relationships.
There has been recent interest in the characterization of soil biodiversity and its function in agricultural grasslands. Much of the interest has come from the need to develop grassland management strategies directed at manipulating the soil biota to encourage a greater reliance on ecosystem self-regulation. This review summarises information on selected groups of soil animals in grasslands, the factors influencing their abundance, diversity and community structure and their relationships to the functioning and stability of grassland ecosystems. Observations on the impacts of agricultural managements on populations and communities of soil fauna and their interactions confirm that high input, intensively managed systems tend to promote low diversity while lower input systems conserve diversity. It is also evident that high input systems favour bacterial-pathways of decomposition, dominated by labile substrates and opportunistic, bacterial-feeding fauna. In contrast, low-input systems favour fungal-pathways with a more heterogeneous habitat and resource leading to domination by more persistent fungal-feeding fauna. In view of this, we suggest that low input grassland farming systems are optimal for increasing soil biotic diversity and hence self-regulation of ecosystem function. Research is needed to test the hypothesis that soil biodiversity is positively associated with stability, and to elucidate relationships between productivity, community integrity and functioning of soil biotic communities.
The trophic preferences of soil invertebrates such as Collembola are often determined by the analysis of gut contents, or through visual observations of the location of individuals. As an alternative approach, two species of Collembola, Folsomia candida and Proisotoma minuta, were offered a choice of the soil fungus Cladosporium cladosporioides or the bacterial feeding nematode Panagrellus redivivus; each exhibited distinct fatty acid profiles and stable carbon isotopic compositions. Over 21 days, the fatty acids i15:0, i17:0, 18:1(n-7) and 18:2(n-6) all increased in abundance in both collembolan species consistent with direct routing from the nematode dietary choice which contained a high concentration of these components. Collembolan fatty acid δ13C values increased by between 5.7 and 21.6‰ over 21 days reflecting those of the nematode diet. Therefore, both fatty acid profiles and δ13C values were consistent with a strong feeding preference of F. candida and P. minuta for the nematodes over the offered fungi. In fact, neither collembolan species consumed any detectable amount of C. cladosporioides. Comparison of the δ13C values of the 16:0 and 18:0 fatty acids (which are biosynthesised by the Collembola as well as directly incorporated from the diet) and the 16:1(n-7) and 18:2(n-6) components (which are not biosynthesised by the Collembola) demonstrated that the input of distinct pools of C can lead to large shifts in δ13C values between diet and consumer. The fatty acids that were not biosynthesised by Collembola better reflected the δ13C values of the diet helping to differentiate between biosynthesised and directly incorporated compounds; an important prerequisite in the interpretation of compound-specific δ13C values in trophic behaviour tests. The combination of fatty acid distributions and δ13C values is a significant improvement on traditional methods of examining feeding preferences, since it determines directly the assimilated dietary carbon rather than relying on indirect observations, such as the proximity of individuals to a defined food source.
Plant roots compete for nutrients mineralised by the decomposer community in soil. By affecting microbial biomass and activity Collembola influence the nutrient availability to plants. We investigated the effect of Collembola (Protaphorura fimata Gisin) on growth and competition between of two plant species, Cirsium arvense L (creeping thistle) and Epilobium adnatum Griseb. (square-stemmed willow herb), in a laboratory experiment. Two seedlings of each plant species were planted in rhizotrons either in combination or in monoculture (intra- and interspecific competition). Interspecific competition strongly reduced total biomass of C. arvense whereas E. adnatum suffered most from intraspecific competition. Collembola neither affected the competitive relationship of the two plant species nor shoot and root biomass. Although Collembola did not affect total root biomass they influenced root morphology of both plant species. Roots grew longer and thinner and had more root tips in presence of Collembola. Root elongation is generally ascribed to the exploitation of nutrient rich patches in soil. We hypothesise that changes in root morphology in presence of Collembola are due to Collembola-mediated changes in nutrient availability and distribution.
Explains isotope terminology and fractionation, and summarises isotopic distributions in the C, N and S biogeochemical cycles. Five case studies (delta 15N measures of N2 fixation; the global carbon cycle and the CO2 problem; sulphur and acid deposition; use in archaeology; and detrital organic matter in saltmarshes) show how stable isotope measurements can provide crucial information for ecosystem analysis.-P.J.Jarvis
Arbuscular mycorrhizal fungi are ubiquitous in field soils, as are mycophagous animals such as Collembola. It has been suggested that these animals reduce the functioning of the mycorrhiza and are thus detrimental to plant growth. However, recent choice experiments suggest that Collembola preferentially feed on nonmycorrhizal fungi in the rhizosphere. If these preferences also occur in field soils, then Collembola might indirectly benefit plants through an enhancement of mycorrhizal functioning and indirect multitrophic links to foliar-feeding insect herbivores.