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The balance between productivity and food web structure in soil ecosystems
... According to ecological theory 18,19) , in order to develop a functioning decomposer food web, that can promote detoxification and site remediation, several factors need to be considered. First, the soil toxicity needs to be reduced sufficiently to support eukaryotes as well as prokaryotes. ...
... The functional groups, or ecological guilds, all need to be present, but they each need to contain a diversity of species. The increased species richness in each functional group is believed to enhance stability and productivity of the food web 19) . Over time, with ecological succession, the species in each functional group change. ...
Land to be remediated, such as those affected by heavy metals or organic pollutants, can be remediated using biological approaches. These include, quarries and strip mines, or land impacted by oil pollution or other organic pollutants. Phytoremediation is usually a key component of bioremediation. However, without restoring soil organic matter, the soil biodiversity takes decades to recover. The soil organisms are a key component of soil function, and support plant growth. In addition, the soil microbiology is essential both for bioremediation and supporting phytoremediation. Using inexpensive sources of quality organic matter, it should be possible to accelerate recovery of ecosystem health and biodiversity. One potential source of untapped organic matter is municipal solid waste as a composted amendment. The organic matter amendment promotes soil structure and the creation of adequate habitat and substrate for the soil decomposition food web. Long-term chronosequence studies indicate that soil food webs tend to make a transition after about 20 years to a stable community structure. This approach could be used to gain carbon credits by restoring degraded or polluted soils.
... Ecosystem engineers (mainly earthworms) produce organo-mineral structures and a large variety of pores, which promotes denitrification, N-fixation, C and N mineralization as well as infiltration of water and air (Lavelle 1996). Consequently, soil fauna drive soil processes strongly affecting agricultural production (de Ruiter et al. 2005). ...
Soil fauna plays an essential role in agricultural productivity as it mediates nutrient cycling and soil organic matter dynamics, alters soil physicochemical properties and supports plant growth. Nitrogen fertilization may have a positive or negative influence on soil fauna in a manner that alters ecosystem functioning, but these links have not yet been quantified. We present the results of a global meta-analysis of available literature data on the effects of N fertilization on taxonomic and ecological groups of soil fauna. Our results show that organic N fertilization increases the density of springtails, mites and earthworms, as well as the biomass of earthworms compared to when no fertilizer is applied. The meta-analysis for different nematode feeding groups and ecological categories of springtails and earthworms as well as different mite orders showed that organic fertilization has an overall positive effect on most groups as opposed to inorganic fertilization, which has neutral or negative effects on most groups, alone or in combination with organic fertilizers. Additional meta-analyses showed that the effects of N fertilization on soil fauna depend on the N application rate, on soil texture and on climatic conditions. Our findings suggest that the adoption of less intense farming practices such as organic fertilization combined with site-specific N fertilization regimes is a suitable strategy for protecting and enhancing functional communities of soil fauna.
... Ecosystem stability can be driven by complex species interactions across trophic levels (Dunne et al. 2002, Hedlund et al. 2004, de Ruiter et al. 2005, as well as individual and community-level responses to perturbations (Loreau et al. 2001, Garcia-Raventós et al. 2017. Generally, communities with more genetic diversity have a greater buffering capacity and, thus, increased versatility toward disturbances such as soil pollution (Atlas et al. 1991) and heat (Wertz et al. 2007), leading to increased stability in times of environmental fluctuations and stress (Loreau et al. 2001, Isbell et al. 2015. ...
Soil microbial community functions are essential indicators of ecosystem multifunctionality in managed land‐use systems. Going forward, the development of adaptation strategies and predictive models under future climate scenarios will require a better understanding of how both land‐use and climate disturbances influence soil microbial functions over time. Between March and November 2018, we assessed the effects of climate change on the magnitude and temporal stability of soil basal respiration, soil microbial biomass and soil functional diversity across a range of land‐use types and intensities in a large‐scale field experiment. Soils were sampled from five common land‐use types including conventional and organic croplands, intensive and extensive meadows, and extensive pastures, under ambient and projected future climate conditions (reduced summer precipitation and increased temperature) at the Global Change Experimental Facility (GCEF) in Bad Lauchstädt, Germany. Land‐use and climate treatment interaction effects were significant in September, a month when precipitation levels slightly rebounded following a period of drought in central Germany: compared to ambient climate, in future climate treatments, basal respiration declined in pastures and increased in intensive meadows, functional diversity declined in pastures and croplands, and respiration‐to‐biomass ratio increased in intensive and extensive meadows. Low rainfall between May and August likely strengthened soil microbial responses toward the future climate treatment in September. Although microbial biomass showed declining levels in extensive meadows and pastures under future climate treatments, overall, microbial function magnitudes were higher in these land‐use types compared to croplands, indicating that improved management practices could sustain high microbial ecosystem functioning in future climates. In contrast to our hypothesis that more disturbed land‐use systems would have destabilized microbial functions, intensive meadows and organic croplands showed stabilized soil microbial biomass compared to all other land‐use types, suggesting that temporal stability, in addition to magnitude‐based measurements, may be useful for revealing context‐dependent effects on soil ecosystem functioning.
... A higher biomass ratio of fungi to bacteria is believed to indicate a more sustainable agro-ecosystem (de Vries et al., 2006). It had also been reported that a clear relationship between increasing plant productivity and bacterial versus fungal dominance (Ingham and Slaughter, 2004;de Ruiter et al., 2005). The earliest descriptions of fungal-dominated and bacterial-dominated microbial communities appeared 40 years ago, where microbial communities in streams were reported to shift from fungal-dominated to bacterial-dominated as litter decomposition proceeded (Bärlocher and Kendrick, 1974;Suberkropp and Klug, 1976). ...
... Gessner et al. (2010) modifiée avecScheu (2002) et de Ruiter et al. (2005 ...
Résumé : Dans le contexte actuel de forte érosion de la biodiversité et de préparation de « l’après pétrole », les forêts apparaissent comme des écosystèmes clés fournissant de nombreux services écosystémiques e.g. capacité de stockage de carbone, production de matières premières et d’énergies renouvelables, biodiversité. Pour les prochaines décennies, un enjeu majeur de la sylviculture sera de développer une gestion forestière durable en termes économique, écologique et patrimoniale, conciliant la préservation des services écosystémiques avec les usages productifs. L’enjeu actuel pour les scientifiques est donc de fournir aux gestionnaires des outils renseignant sur la manière dont les futures orientations sylvicoles vont concilier usages productifs et fonctionnement des écosystèmes forestiers. Les recherches présentées ici portent sur l’étude des relations entre peuplements forestiers, communautés biologiques (microflore, mésofaune, macrofaune) de l’interface sol-végétation et fonctionnement de cette dernière (minéralisation de l’N, décomposition des litières, stock de C). Le modèle biologique étudié est la hêtraie pure gérée en futaie régulière et considérée dans l’ensemble de sa rotation sylvicole depuis les fourrés jusqu’au stade de régénération. L’objectif principal est de caractériser les leviers biologiques régulant et/ou orientant l’effet du compartiment végétal sur le fonctionnement biologique de l’interface sol-végétation au cours de la dynamique du système. La finalité de ses recherches est de fournir un modèle de trajectoire dynamique des relations peuplement forestier – fonctionnement de l’interface sol végétation afin d’utiliser ce dernier comme modèle de référence dynamique pour l’étude de l’effet de la gestion forestière sur la trajectoire dynamique de l’interface sol-végétation. Ces recherches montrent que les vieilles futaies de hêtre (130 ans) à canopée fermée semblent des stades clé de la rotation sylvicole au cours desquels le système rebascule de la phase autotrophe à la phase hétérotrophe. Durant la phase autotrophe (maturation des peuplements depuis 15 ans jusqu’à 95 ans), le fonctionnement de l’interface sol-végétation semble bien régulé et orienté par le peuplement forestier de hêtres. Biologiquement, le hêtre favorise, via la qualité de sa litière et son système racinaire ectomycorhizé, l’augmentation de la biomasse fongique et la diversité métabolique des bactéries hétérotrophes. Fonctionnellement ceci se traduit par un ralentissement de la vitesse de décomposition de la litière et l’inhibition de la nitrification autotrophe conduisant à une production d’ammonium plus importante. Dans les vieilles futaies fermées de 130 ans, l’amélioration significative de la qualité de la litière de hêtre se traduit par l’apparition de fonctions métaboliques bactériennes nouvelles et une amélioration de la vitesse de décomposition des feuilles suggérant le basculement du système vers la phase hétérotrophe du cycle durant laquelle l’activité des biocénoses du sol va conduire la formation de formes d’humus de type mull favorables à la régénération des peuplements. D’un point de vu appliqué, ces résultats ajouté à la spécificité de certaines espèces de collemboles ou de vers de terre pour les parcelles âgée à canopée fermée ou bien le fait que la coexistence des espèces au sein des communautés floristiques, bryophytiques (corticole), de la mésofaune ou de la macrofaune du sol semblent basée sur des mécanismes de coexistence à l’équilibre dans ce type parcelle militent pour ne pas raccourcir la rotation en deçà de 130 ans et pour conserver l’ambiance forestière jusqu’à cet âge. Enfin, l’utilisation du modèle dynamique de référence pour caractériser les effets de la gestion sylvicole sur le fonctionnement biologique de l’interface sol-végétation est illustrée dans les perspectives de travail.
https://hal.archives-ouvertes.fr/tel-01304671/document
... Conversely, loss of SOC will impair a soil's productivity through reduced levels of ecosystem services (Brady et al. 2015). The SOC content of a soil is also relevant to the functioning of soil food webs and water holding capacity, amongst others (Saxton and Rawls 2006;de Ruiter et al. 2005). Therefore, for these reasons and practicality, we use SOC content as a proxy for the stock of soil natural capital. ...
Farmers are exposed to substantial weather and market related risks. Rational farmers seek to avoid large losses. Future climate change and energy price fluctuations therefore make adaptating to increased risks particularly important for them. Managing soil natural capital—the capacity of the soil to generate ecosystem services of benefit to farmers—has been proven to generate the double dividend: increasing farm profit and reducing associated risk. In this paper we explore whether managing soil natural capital has a third dividend: reducing the downside risk (increasing the positive skewness of profit). This we refer to as the prudence effect which can be viewed as an adaptation strategy for dealing with future uncertainties through more prudent management of soil natural capital. We do this by developing a dynamic stochastic portfolio model to optimize the stock of soil natural capital—as indicated by soil organic carbon (SOC) content—that considers the mean, variance and skewness of profits from arable farming. The SOC state variable can be managed by the farmer only indirectly through the spatial and temporal allocation of land use. We model four cash crops and a grass ley that generates no market return but replenishes SOC. We find that managing soil natural capital can, not only improve farm profit while reducing the risk, but also reduce the downside risk. Prudent adaptation to future risks should therefore consider the impact of current agricultural management practices on the stock of soil natural capital.
... To value soil natural capital an indicator of flows of supporting soil ecosystem services is needed, as measuring changes in the biodiversity that mediates services is far from straightforward, due to the complexity of soil food webs and knowledge gaps regarding the specific functions of the multitudes of different organisms inhabiting arable soils (Bardgett et al., 2005;de Vries et al., 2013). Soil organic carbon (SOC) is here used as a proxy for soil biodiversity as it is correlated with soil biodiversity and food webs (de Ruiter et al., 2005;Tsiafouli et al., 2015), as well as a number of supporting ecosystem services (Endale et al., 2010;Williams and Hedlund, 2014). Furthermore, SOC is generally considered a major factor in a soil's overall health and agricultural productivity (Johnston et al., 2009). ...
Soil biodiversity through its delivery of ecosystem functions and attendant supporting ecosystem services—benefits soil organisms generate for farmers—underpins agricultural production. Yet lack of practical methods to value the long‐term effects of current farming practices results, inevitably, in short‐sighted management decisions. We present a method for valuing changes in supporting soil ecosystem services and associated soil natural capital—the value of the stock of soil organisms—in agriculture, based on resultant changes in future farm income streams. We assume that a relative change in soil organic C (SOC) concentration is correlated with changes in soil biodiversity and the generation of supporting ecosystem services. To quantify the effects of changes in supporting services on agricultural productivity, we fitted production functions to data from long‐term field experiments in Europe and the United States. The different agricultural treatments at each site resulted in significant changes in SOC concentrations with time. Declines in associated services are shown to reduce both maximum yield and fertilizer‐use efficiency in the future. The average depreciation of soil natural capital, for a 1% relative reduction in SOC concentration, was 144 € ha⁻¹ (SD 47 € ha⁻¹) when discounting future values to their current value at 3%; the variation was explained by site‐specific factors and the current SOC concentration. Moreover, the results show that soil ecosystem services cannot be fully replaced by purchased inputs; they are imperfect substitutes. We anticipate that our results will both encourage and make it possible to include the value of soil natural capital in decisions.
... Swift et al. 2004 ). Thus, de Ruiter et al. ( 2005 ) have shown that stability of the soil ecosystem is closely linked to the relative abundance of the different functional groups of organisms. Soil macrofauna (e.g. ...
What can ecological science contribute to the sustainable management and conservation of the natural systems that underpin human well-being? Bridging the natural, physical and social sciences, this book shows how ecosystem ecology can inform the ecosystem services approach to environmental management. The authors recognise that ecosystems are rich in linkages between biophysical and social elements that generate powerful intrinsic dynamics. Unlike traditional reductionist approaches, the holistic perspective adopted here is able to explain the increasing range of scientific studies that have highlighted unexpected consequences of human activity, such as the lack of recovery of cod populations on the Grand Banks despite nearly two decades of fishery closures, or the degradation of Australia's fertile land through salt intrusion. Written primarily for researchers and graduate students in ecology and environmental management, it provides an accessible discussion of some of the most important aspects of ecosystem ecology and the potential relationships between them.
... This is because the utilization of soil organic matter as a substrate of energy by soil organisms underpins the generation of soil ecosystem services (Bauer and Black, 1994) and, consequently, loss of organic carbon will diminish a soil's capacity to generate services. The carbon content of a soil is also related to the size, complexity and functioning of soil food webs (de Ruiter et al., 2005). Therefore a change in SOC content can be used as a proxy for changing stocks of soil capital. ...
Uncontrollable events such as adverse weather and volatile prices present considerable risks for arable
farmers. Soil natural capital, which views the capacity of soil biodiversity to generate ecosystem services
as a component of farm capital, could be important for the stability and resilience of arable production
systems. We investigate therefore whether managing soil natural capital could be an effective strategy
for mitigating future agricultural risks. We do this by constructing a dynamic stochastic portfolio model
to optimize the stock of soil organic carbon (SOC)—our indicator of soil natural capital—when considering
both the risks and returns from farming. SOC is controlled via the spatial and temporal allocation of cash
crops and an illustrative replenishing land use. We find that higher soil natural capital buffers yield variance
against adverse weather and reduces reliance on external inputs. Managing soil natural capital has
therefore the potential to mitigate two serious agricultural risks: energy price shocks and adverse
weather events, both of which are likely to be exacerbated in the future due to, e.g., globalization and climate
change.
... 1016/j.apsoil.2010.08.014 et al., 1998Bardgett et al., 1999;De Deyn et al., 2003;Bonkowski, 2004). Therefore, their biodiversity, community composition, and trophic structure can provide important insights regarding many aspects of ecosystem function (De Ruiter et al., 2005). ...
Woody plant encroachment into grasslands generally increases spatial heterogeneity of soil properties and processes and creates “islands of fertility” beneath woody canopies. However, little is known regarding the potential for these changes to influence spatial variation in soil fauna. We quantified population sizes, biodiversity, and trophic structure of soil nematode communities in a savanna parkland where woody plant clusters developed in grassland during the past century. Total nematode density was constant across transects from centers of woody clusters into grasslands. Family richness and Simpson's Dominance Index indicated nematode communities in grasslands and grassland/cluster edges were significantly more diverse than positions within the woody clusters. Relative densities of all nematode trophic groups changed significantly along the transect. Bacterivores nearly doubled in relative density from grassland (35%) to cluster centers (60%), apparently in response to higher concentrations of soil microbial biomass in wooded areas. Relative densities of plant parasitic nematodes decreased along transects from grasslands (35%) to centers of woody clusters (10%), implying decreased nematode herbivory in woody clusters despite much higher root biomass there. The structure index indicated nematode communities within woody clusters were more simplified than those in grassland and edge communities due to reductions in densities of omnivores and predators. Although nematode densities were lower at 10–20 than 0–10cm, nematode community characteristics were generally similar between soil depths. Changes in nematode community and trophic structure described here could influence biogeochemical processes, species interactions, and successional processes in regions where woody plants are encroaching into grasslands.
... Understanding nutrient flow is a central goal of both organismal biology and ecosystem ecology but only few models link the flows of carbon and nitrogen through groups of organisms (de Ruiter et al. 2005;Hungate et al. 1997). We modelled the direct release of NH 4 +-N by collembolans in the barley (Paper I) and wheat (Paper II) microcosm studies and concluded that their direct release of readily available plant nutrients was very small (<0.5 % of total plant nitrogen). ...
... Soil organisms are interconnected by a complex web of trophic relationships (Scheu and Falca 2000;Scheu and Setälä 2002;Wardle 2002;De Ruiter et al. 2005;Brussaard et al. 2007). Important trophic groups are litter feeders (saprophages), fungal and bacterial feeders (microphytophages) and predators and Schaefer and Scheu 1996) parasites (zoophages) (Schaefer 1996). ...
The organic remains of plants and animals on the soil surface or in the soil are termed litter. This includes leaves, twigs,
fruits, fructescences, bracts, scales of buds, bark flakes and even whole trees, dead roots, carrion and other resource types.
Dead materials still attached to the living plants are distinguished from litter as ‘standing dead’. Comprehensive reviews
of plant litter decomposition are given by Swift et al. (1979), Cadisch and Giller (1997), Lavelle and Spain (2001) and Laskowski
et al. (2006). A special – mainly fungal – flora associated with living or senescent plant tissue initiates decomposition
before plant litter originates and enters the soil subsystem. On the soil, leaching of low molecular weight compounds takes
place; this material is fairly rapidly mineralised by bacteria and “sugar fungi”. The remaining organic matter is degraded
by further saprotrophic organisms – fungi, bacteria and saprophagous animals. Fungi, in particular Basidiomycetes, are generally
believed to be the most important decomposers of structural plant compounds, e.g. cellulose and especially lignin. The decomposition
subsystem performs two major functions: the mineralisation of essential plant nutrients and the formation of soil organic
matter (Swift et al. 1979; Lavelle and Spain 2001).
... They are the most numerous soil mesofauna and are found in all ecosystems (Ritz and Trudgill, 1999). Nematodes occupy all consumer trophic levels within the soil food web and, therefore, their community composition can lead to insights regarding the structure and function of the soil ecosystem (De Ruiter et al., 2005). Additionally, nematode populations react quickly to disturbance (Bongers, 1999) and can be used to differentiate the effects of management practices (Freckman and Ettema, 1993;Neher and Campbell, 1994); therefore, several indexes have been developed to assess the structure and function of the nematode community following environmental change (Bongers, 1990;Ferris et al., 2001). ...
Soil food web structure is an integral component of ecosystem function, but there are few strategies orientated towards managing its development in restoration projects. The objective of this study was to direct nematode community structure and function through the application of organic amendments to the soil of an urban landfill remediation project using native grassland vegetation. We used a 2 × 3 factorial design in which an organic amendment was added to the soil at different locations (incorporated versus surface-applied) and amounts (none, light, heavy). Nematode and plant community structure were monitored over three growing seasons to determine the rate and direction of change. Surface application of organic amendments supported greater grass and total plant densities compared to incorporated amendment treatments, but plant density did not vary with amendment amount. Total nematode density, family diversity and family richness were not affected by the amendment treatments, but both family richness and seasonal nematode density increased over the duration of the experiment. Other descriptors of nematode community development (Structure, Maturity, and Plant Parasite Indexes) were not influenced by either amendment amount or location, but varied significantly over time. Contrary to expectations, the surface amendment treatments significantly increased bacterivorous, plant parasitic, omnivorous and predator nematode densities, but had no influence on fungi/root-tip feeding nematodes. Also contrary to our hypotheses, the surface treatments had smaller Channel Index and greater Enrichment Index values relative to the incorporated treatments during the first 15 month of the experiment. We hypothesize that the surface amendments are indirectly affecting the structure of the nematode community by promoting greater plant density, thus increasing the concentration of high-quality organic matter (such as root exudates) in the soil. This promotes the development of a nematode community dominated by opportunistic groups that respond rapidly to increased resource availability. Future studies should aim to distinguish between the organic amendment's direct function as a potential food source for the soil biota versus their indirect role as an environmental variable, including their capability to alter the availability of plant-derived resources.
... Decomposer biota, including microbes and invertebrate fauna, play a pivotal role in litter decomposition and through their feeding activity drive the amount and timing of organic matter turnover and mineral nutrient availability (Seastedt, 1984; Beare et al., 1992; Hunter et al., 2003). Control over the availability of resources for plant productivity forms a feedback from belowground systems to aboveground processes and communities (De Ruiter et al., 2005). Recently, there has been increasing interest in effects that operate in the opposite direction. ...
Inputs of aboveground plant litter influence the abundance and activities of belowground decomposer biota. Litter-mixing studies have examined whether the diversity and heterogeneity of litter inputs affect decomposer communities in ways that can be predicted from monocultures. They have mainly attempted to detect non-additive effects of litter mixing, although individual species effects (additivity) as well as species interactions (non-additivity) may alter decomposition rates. To determine potential impacts of plant species loss on aboveground-decomposer linkages, we assessed both additive and non-additive effects of litter mixing on decomposer communities. A full-factorial litterbag experiment with leaves from four deciduous tree species was conducted, to assess responses of bacteria, fungi, nematodes, and microarthropods. Data were analyzed using a statistical method that first looked for additive effects based on the presence or absence of species and then any significant species interactions. We observed almost exclusively additive effects of all four litter species on decomposer biota, with each species exerting effects on different aspects of the community. These results imply that the consequences of species loss for the decomposer community will be largely predictable from knowledge of single species litter dynamics. The two species at opposite ends of the quality spectrum exerted the most effects. High-quality Liriodendron tulipifera supported a more diverse arthropod community and drove bottom-up effects on the decomposer food web. Low-quality Rhododendron maximum had negative effects on most groups of biota. Litter of mid-quality species exerted fewer effects. The influence of litter species richness on the Tylenchidae (nematodes) was the only non-additive effect of litter mixing. Together, these data demonstrate an effect of plant community composition on decomposer biomass, abundance, and diversity, confirming a link between above and belowground communities. We were able to identify the species to which the decomposer community is most sensitive, aiding predictions of the consequences of the loss of these dominant species on the decomposer community, with potential feedbacks for organic matter and nutrient turnover.
... Nematodes are of particular interest because they are the most numerous soil mesofauna and occupy all consumer trophic levels within the soil food web. Therefore, their community structure can provide important insights regarding many aspects of ecosystem function (De Ruiter et al., 2005). ...
Woody plant encroachment is an important land cover change in dryland ecosystems throughout the world, and frequently alters above and belowground primary productivity, hydrology, and soil microbial biomass and activity. However, there is little known regarding the impact of this geographically widespread vegetation change on the biodiversity and trophic structure of soil fauna. Nematodes represent a major component of the soil microfauna whose community composition and trophic structure could be strongly influenced by the changes in ecosystem structure and function that accompany woody encroachment. Our purpose was to characterize nematode community composition and trophic structure along a grassland to woodland chronosequence in the Rio Grande Plains of southern Texas. Research was conducted at the La Copita Research Area where woody encroachment has been documented previously. Soil cores (0–10 cm) were collected in fall 2006 and spring 2007 from remnant grasslands and woody plant stands ranging in age from 15 to 86 years, and nematodes were extracted by sugar centrifugation. Neither nematode densities (3200–13,800 individuals kg−1 soil) nor family richness (15–19 families 100 g−1 soil) were altered by woody encroachment. However, family evenness decreased dramatically in woody stands >30 years old. This change in evenness corresponded to modifications in the trophic structure of nematode communities following grassland to woodland conversion. Although root biomass was 2–5× greater in wooded areas, root-parasitic nematodes decreased from 40% of all nematodes in grasslands to <10% in the older wooded areas, suggesting the quality (C:N or biochemical defenses) of woody plant root tissue could be limiting root-parasites. In contrast, bacterivores increased from 30% of nematodes in grasslands to 70–80% in older woody patches. This large increase in bacterivores may be a response to the 1.5–2.5× increase in soil microbial biomass (bacteria + fungi) following woody encroachment. Therefore, while energy flow through grassland nematode communities appears to be distributed nearly equally among herbivory, fungivory and bacterivory, the energy flow through nematode communities in wooded areas appears to be based primarily on bacterivory. We speculate that these shifts in nematode community composition and trophic structure could have important implications for ecosystem patterns and processes. First, the low abundance of root-parasitic nematodes (and presumably root herbivory) under woody plants may be one mechanism by which woody plants are able to establish and compete effectively with grasses during succession from grassland to woodland. Second, the large increase in bacterivores following woody encroachment likely accelerates microbial turnover and the mineralization of N, thereby providing a feedback that enables the persistence of N-rich woody plant communities.
Soil fauna plays an essential role in agricultural productivity as it mediates nutrient cycling and soil organic matter dynamics, alters soil physicochemical properties and supports plant growth. Nitrogen fertilization may have a positive or negative influence on soil fauna in a manner that alters ecosystem functioning, but these links have not yet been quantified in a generalized manner. We present the results of a global meta-analysis of available literature data on the effects of nitrogen fertilization on taxonomic and ecological groups of soil fauna. Our results show that nitrogen fertilization increases the abundance of nematodes (+36%), springtails (+29%), mites (+35%), and the biomass of earthworms (+15%) compared to when no fertilizer is applied. The meta-analysis for different nematode feeding groups and life-form groups of springtails, mites and earthworms showed that organic fertilization has an overall positive effect on most taxonomic groups as opposed to inorganic fertilization, which has neutral or negative effects on most taxonomic groups. Additional meta-analyses showed that the effects of nitrogen fertilization on soil fauna depend on the intensity of the fertilization regime, on soil physicochemical properties as well as on climatic conditions. Our findings suggest that the adoption of less intense farming practices such as organic fertilization combined with site-specific nitrogen fertilization regimes is a suitable strategy for protecting and enhancing functional communities of soil fauna.
Aims
Global environmental changes are known to affect terrestrial ecosystems. However, how plants and soil microorganisms respond to warming and nitrogen deposition in a desert steppe with strong seasonal drought remains largely unexplored.
Methods
Based on a 13-year manipulative field experiment, we investigated the effects of warming and nitrogen addition on soil microbial communities and plant net photosynthetic rates during two hydrologically contrasting months (6 mm in June and 106 mm in July) in a desert steppe in Inner Mongolia.
Results
We found that in the wet month, warming and nitrogen (N) addition significantly increased soil microbial biomass. Warming and N addition significantly increased soil inorganic N and increased leaf N concentration, thus promoting the net photosynthetic rate of Stipa breviflora. Moreover, warming and N addition significantly shifted soil microbial composition with an increase in soil bacterial phospholipid fatty acids (PLFAs) and reduced fungal PLFAs. The increased soil inorganic N indirectly increased leaf N and plant photosynthesis by soil microbial composition. These changes were not significant in the dry month.
Conclusions
Our study indicates that warming and N addition can promote plant photosynthesis by increasing soil N availability and changing the structure of the soil microbial community. These changes only occurred when there was sufficient precipitation. These results highlight the crucial role of soil water availability and the soil microbial community in influencing plant responses to global change drivers (e.g., warming and N addition).
While much is known regarding the development of plant communities during primary succession and concomitant pedogenesis, considerably less is known regarding the development of soil microbial and soil fauna communities. In view of the importance of soil biota to soil processes, the nature of the belowground ecosystem and its development during pedogenesis is reviewed and discussed using recent chrono,sequence studies. During primary succession plant communities characteristically turnover several times. By contrast, community development for soil biota is characterized by progressive addition with many pioneer species remaining throughout soil development. In general, the size and diversity of soil biotic communities increases rapidly during the first 20-50 years and then more or less stabilizes after hundreds of years, while plant biomass and soil organic matter content do not reach a peak for many hundreds or even thousands of years. The development of the soil faunal community is less rapid than that of the microbial community because dispersal is slower and in addition some faunal species require a certain depth of organic topsoil and/or litter layer before high populations develop. With increasing successional time the food web (based on organic detritus) becomes increasingly complex. Based on the reviewed data, a conceptual model of changes in plant, soil microbial, and soil faunal communities that occur during succession is presented. The significance of such changes to restoration of unweathered mine tailings is also discussed.
General circulation models on global climate change predict increase in surface air temperature and changes in precipitation. Increases in air temperature (thus soil temperature) and altered precipitation are known to affect the species composition and function of soil microbial communities. Plant roots interact with diverse soil organisms such as bacteria, protozoa, fungi, nematodes, annelids and insects. Soil organisms show diverse interactions with plants (eg. competition, mutualism and parasitism) that may alter plant metabolism. Besides plant roots, various soil microbes such as bacteria and fungi can produce volatile organic compounds (VOCs), which can serve as infochemicals among soil organisms and plant roots. While the effects of climate change are likely to alter both soil communities and plant metabolism, it is equally probable that these changes will have cascading consequnces for grazers and subsequent food web components aboveground. Advances in plant metabolomics have made it possibile to track changes in plant metabolomes as they respond to biotic and abiotic environmental changes. Recent developments in analytical instrumentation and bioinformatics software have established metabolomics as an important research tool for studying ecological interactions between plants and other organisms. In this review, we will first summarize recent progress in plant metabolomics methodology and subsequently review recent studies of interactions between plants and soil organisms in relation to climate change issues.
Although Sikkim belongs to one of the Global Biodiversity Hotspots, little is known about its ectomycorrhizal fungi, and even less about the main genera of Russulales, i.e. Lactarius, Lactifluus, Multifurca and Russula. Combining a multilocus genealogical and morphological study, we aimed to document the diversity within Lactifluus volemus sensu lato of Sikkim Himalaya. We compared nuclear ITS and LSU rDNA, nuclear rpb1 and rpb2 protein-coding, and mitochondrial atp6 protein-coding genealogies to determine species boundaries. Interspecific relationships were inferred from the combined dataset. Bayesian and maximum likelihood single-locus genealogies are concordant and support recognition of six species. Three of these could be identified by unique morphological characteristics and are described as new species: L. dissitus, L. leptomerus and L. versiformis.
We critically highlight some evidence for the importance of soil biodiversity to sustaining (agro-)ecosystem functioning and explore directions for future research. We first deal with resistance and resilience against abiotic disturbance and stress. There is evidence that soil biodiversity does confer stability to stress and disturbance, but the mechanism is not yet fully understood. It appears to depend on the kind of stress and disturbance and on the combination of stress and disturbance effects. Alternatively, community structure may play a role. Both possible explanations will guide further research. We then discuss biotic stress. There is evidence that soil microbial diversity confers protection against soil-borne disease, but crop and soil type and management also play a role. Their relative importance as well as the role of biodiversity in multitrophic interactions warrant further study. Henceforth, we focus on the effects of plant and soil biodiversity on nutrient and water use efficiencies as important ecological functions in agroecosystems. The available evidence suggests that mycorrhizal diversity positively contributes to nutrient and, possibly, water use efficiency. Soil fauna effects on nutrient and water use efficiencies are also apparent, but diversity effects may be indirect, through effects on soil structure. We present a conceptual diagram relating plant and soil biodiversity with soil structure and water and nutrient use efficiencies as a framework for future studies. We then consider how cropping systems design and management are interrelated and how management options might be interfaced with farmers’ knowledge in taking management decisions. Finally, we attempt to express some economic benefits of soil biodiversity to society as part of a wider strategy of conserving and using agrobiodiversity.
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