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Soil fungi promote nitrogen transfer among plants involved in long-lasting facilitative interactions
... In arid and semiarid ecosystems, AMF promote the establishment and survival of their hosts by enhancing drought tolerance and buffering low soil fertility (Smith et al. 2010; Barea et al. 2011). Also, their mycelium increases soil aggregation (Chaudhary et al. 2009) and promotes the redistribution of N from RIs-forming plants to those plants that coexist into the RIs by interconnecting their roots (Montesinos-Navarro et al. 2016;. Thus, AMF are critical for formation of RIs (Carrillo- García et al. 1999;Montesinos-Navarro et al. 2012a, b;Sortibrán et al. 2019), as well as for growth biology of woody plants belonging to legumes such as Mimosoideae (Camargo-Ricalde et al. 2010b); however, it is still necessary to examine how woody Mimosoideae species and rainfall influence the AMF communities into the RIs formed within these dry environments. ...
... RIs-forming plants, together with AMF, make up the plant-RI-AMF system, as demonstrated in the case of Mimosa luisana (Leguminosae), a woody nurse plant that benefits from its facilitated plants, and in turn transfers to them N through arbuscular mycorrhiza (Montesinos-Navarro et al. 2016;Sortibrán et al. 2019). What remains unknown, however, is how AMF communities in this system (Mimosa-RI-AMF) are altered by the identity of the woody Mimosa species, whether or not it is RI-forming (Mimosa-RI vs Mimosa-NRI), and in the different environmental contexts that occur in these ecosystems. ...
... The Mimosa-RIs studied did not favour the mycorrhizal inoculum potential of the soil compared to the OAs and M. purpusii-NRIs, so this potential might depend more on mycelium biomass than on spore abundance or AMF species richness and composition, but this hypothesis remains to be tested. Finally, endemic Mimosa species here studied forming or not resource islands jointly with rainfall seasonality modulated AMF communities, in turn the biology of these woody species and their mycorrhizal symbionts must be documented, as it could have implications for facilitation and coexistence of plants (Montesinos-Navarro et al. 2012a,b), soil aggregation and stabilisation (Chaudhary et al. 2009), and nutrient cycling (Montesinos-Navarro et al. 2016;. ...
Key message
Woody Mimosa species, forming resource islands or not, affected the structure of mycorrhizal communities and increased soil fertility, being thus priority targets for conservation and reclamation of edaphic functions.
Abstract
In arid and semiarid ecosystems woody plants forming resource islands (RIs) contribute to improve soil fertility; however, its effect on arbuscular mycorrhizal fungi (AMF) communities is little known. The objectives of this study were to: (1) characterize the AMF communities and their mycorrhizal potential in soil associated to four woody species of Mimosa, three that are RIs-forming (M. lacerata, M. luisana and M. polyantha) and one that is not (M. purpusii-NRIs) compared to open areas (OAs) without plants; and (2) determine the relationship between AMF and soil properties in two seasons (rainy and dry) in the semiarid Tehuacán–Cuicatlán Valley (TCV), Puebla and Oaxaca, Mexico. All Mimosa species favoured AMF richness and spore abundance and altered AMF composition, but to varying degrees depending on the Mimosa species. The three Mimosa species forming RIs and M. purpusii-NRIs improved soil conditions and resources to a similar extent as compared to OAs changing thus AMF species composition; however, only the RIs of M. luisana and M. polyantha did promote AMF diversity under conditions of greater disturbance in the vegetation structure. In contrast, these Mimosa species did not increase mycorrhizal inoculum potential compared to OAs. In addition, the rainfall seasonality affected the fungal community mostly in M. luisana-RI and M. polyantha-RI than in M. lacerata-RI and M. purpusii-NRI. In conclusion, these four Mimosa species, RIs-forming or not, affected AMF communities and soil fertility, being thus priority targets for conservation and reclamation of edaphic functions that perform these fungi within semiarid TCV, so the biology of these woody plants and their symbionts must be better documented.
... The transfer of fixed N from N 2 -fixers to neighboring plants is affected by many factors. Montesinos-Navarro et al. (2016) reported that common mycorrhizal relationships could enhance N transfer among adult plants. Additionally, the extent of nodule turnover and the size of the root system, through their effect on the amounts of rhizodeposited N and the incidence of mycorrhizal fungi, are likely to affect N transfer (Moyer-Henry et al. 2006;Phillips, Fox, and Six 2006;Rasmussen et al. 2007). ...
... It has been reported that decomposition of N 2 -fixers aboveground litter and exudation of soluble N compounds from N 2 -fixers may contribute to decreased soil δ 15 N where clover is planted, which is considered the important pathway of fixed N transfer (Paynel et al. 2008;He et al. 2009;Munroe and Isaac 2014). Additionally, common mycorrhizal networks have been suggested as a potential mechanism for N transfer from N 2 -fixers to non-N 2 -fixing plants (Montesinos-Navarro et al. 2016). Montesinos-Navarro et al. (2016) also suggest that this fixed-N transfer pathway, mediated by mycorrhizal fungi, is more effective than via root exudates from the N 2 -fixers in the short term. ...
... Additionally, common mycorrhizal networks have been suggested as a potential mechanism for N transfer from N 2 -fixers to non-N 2 -fixing plants (Montesinos-Navarro et al. 2016). Montesinos-Navarro et al. (2016) also suggest that this fixed-N transfer pathway, mediated by mycorrhizal fungi, is more effective than via root exudates from the N 2 -fixers in the short term. It was suggested that 46-60% of N uptake by the grass in a two-year grass-clover ley was clover fixed N (Oberson et al. 2013). ...
Biological nitrogen fixation (BNF) is an important nitrogen source for both N 2-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N 2-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with 15 N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N 2 fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant −1 , which was significantly lower than that of the CN (6.18 mg N plant −1) and HW (8.01 mg N plant −1) soils. Nitrogen in grass sourced from BNF via below-ground was 0.46 mg N plant −1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.
... Similarly, the nurse Mimosa luisana produces more and better seeds when growing associated to its facilitated species in phylogenetically diverse neighbourhoods (Sortibr an et al. 2014), while the facilitated species receive N from the nurse (Montesinos-Navarro et al. 2016, 2017. Positive effects of facilitated plants on nurses would explain the maintenance of facilitative interactions until adult stages in vegetation patches, and such effects could be mediated by mycorrhizal fungi . ...
... Mycorrhizal fungi can transport water, nutrients and chemical defences from facilitated plants directly to their nurses through common mycorrhizal networks (Newman 1988;Selosse et al. 2006;Simard et al. 2012;Gorzelak et al. 2015) or indirectly through hydraulic lift or hyphal exudates (Querejeta et al. 2003;Finlay 2008;Zhang et al. 2016). Direct transfer of nutrients and water between plant roots through mycorrhizal networks has been extensively documented (Giovannetti et al. 2004;Egerton-Warburton et al. 2007;Mikkelsen et al. 2008;Simard et al. 2012;Montesinos-Navarro et al. 2016), but its ecological role on the outcome of plant-plant interactions and community dynamics is still debated (Van der Heijden & Horton 2009;Bever et al. 2010). Indirect transfer may also occur as mycorrhizal fungi can move water from roots to soil, enhancing the magnitude of hydraulic lift and making water available for other plants (Querejeta et al. 2003;Prieto et al. 2012). ...
... Mimosa luisana is the generalist species with the largest number of partners in the plant-AMF community network (Montesinos-Navarro et al. 2012b). Likewise, there is evidence that AMF promote N transfer from M. luisana to its facilitated species (Montesinos-Navarro et al. 2016), thus making it possible for facilitated species to reciprocate their benefits with the nurse through mycorrhizal fungi during the ontogeny of the interacting plants. We experimentally applied a fungicide to reduce AMF abundance in M. luisana nurses growing both in isolation and associated with their facilitated plants and evaluated the effect on its different fitness components (reproductive success). ...
Plant facilitation promotes coexistence by maintaining differences in the regeneration niche because some nurse species recruit under arid conditions, whereas facilitated species recruit under more mesic conditions. In one Mexican community, 95% of species recruit through facilitation, being Mimosa luisana a keystone nurse for many of them. M. luisana individuals manifest greater fitness when growing in association with their facilitated plants than when growing in isolation. This observation suggests that nurses also benefit from their facilitated plants, a benefit thought to be mediated by mycorrhizal fungi.
Under field conditions, we experimentally tested whether mycorrhizal fungi mediate the increased fitness that M. luisana experiences when growing in association with its facilitated plants. We applied fungicide to the soil for nurse plants growing alone and growing in association with their facilitated plants in order to reduce the mycorrhizal colonization of roots. We then assessed the quantity and quality of seed production of M. luisana in four treatments (isolated‐control, isolated‐fungicide, associated‐control and associated‐fungicide).
Fungicide application reduced the percent root length colonized by mycorrhizae and reduced fitness of M. luisana when growing in association with their facilitated plants but not when growing in isolation. This reduction was reflected in the total number of seeds, number of seeds per pod, seed mass and seed viability.
These results suggest that nurses are benefitting from the presence of their facilitated plants through links established by mycorrhizae, indicating that both plants and belowground, mutualistic communities are all part of one system, coexisting by means of intrinsically linked interactions.
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... Belowground facilitation occurs when one species makes previously unavailable P available to the other, due to the exudation of organic acids, phosphatases, or rhizosphere acidification resulting in increased P availability (Hinsinger et al., 2011). Since a decade ago, numerous studies have also pointed to the importance of soil-borne arbuscular mycorrhizal (AM) fungi of the phylum Glomeromycota (Tedersoo et al., 2020) in mediating inter-plant facilitation processes (van der Heijden et al., 2008;Montesinos-Navarro et al., 2016). In soils with strong Pi-fixing capacity, or where Pi is limiting, plant demand for this nutrient exceeds the rate at which it diffuses into the root zone, resulting in zones of Pi depletion surrounding the roots (Smith and Read, 1997). ...
... The role of AM fungi in mixed plant communities is applicable due to their low host specificity: extra-radical hyphae can connect the roots of different plant species to form a common mycelial network (CMN) (Ingleby et al., 2007). This inter-plant mycorrhizal connection promotes facilitation through differential access to the nutrient pool from the common hyphal network and plant-to-plant nutrient transfers (Fitter et al., 1998;Martins and Cruz, 1998;Leake et al., 2004;Simard and Durall, 2004;Hauggaard-Nielsen and Jensen, 2005;Ingleby et al., 2007;van der Heijden and Horton, 2009;de Carvalho et al., 2010;Walder et al., 2012;Fellbaum et al., 2014;Gorzelak et al., 2015;Montesinos-Navarro et al., 2016). ...
Under agroforestry practices, inter-specific facilitation between tree rows and cultivated alleys occurs when plants increase the growth of their neighbors especially under nutrient limitation. Owing to a coarse root architecture limiting soil inorganic phosphate (Pi) uptake, walnut trees (Juglans spp.) exhibit dependency on soil-borne symbiotic arbuscular mycorrhizal fungi that extend extra-radical hyphae beyond the root Pi depletion zone. To investigate the benefits of mycorrhizal walnuts in alley cropping, we experimentally simulated an agroforestry system in which walnut rootstocks RX1 (J. regia x J. microcarpa) were connected or not by a common mycelial network (CMN) to maize plants grown under two contrasting Pi levels. Mycorrhizal colonization parameters showed that the inoculum reservoir formed by inoculated walnut donor saplings allowed the mycorrhization of maize recipient roots. Relative to non-mycorrhizal plants and whatever the Pi supply, CMN enabled walnut saplings to access maize Pi fertilization residues according to significant increases in biomass, stem diameter, and expression of JrPHT1;1 and JrPHT1;2, two mycorrhiza-inducible phosphate transporter candidates here identified by phylogenic inference of orthologs. In the lowest Pi supply, stem height, leaf Pi concentration, and biomass of RX1 were significantly higher than in non-mycorrhizal controls, showing that mycorrhizal connections between walnut and maize roots alleviated Pi deficiency in the mycorrhizal RX1 donor plant. Under Pi limitation, maize recipient plants also benefited from mycorrhization relative to controls, as inferred from larger stem diameter and height, biomass, leaf number, N content, and Pi concentration. Mycorrhization-induced Pi uptake generated a higher carbon cost for donor walnut plants than for maize plants by increasing walnut plant photosynthesis to provide the AM fungus with carbon assimilate. Here, we show that CMN alleviates Pi deficiency in co-cultivated walnut and maize plants, and may therefore contribute to limit the use of chemical P fertilizers in agroforestry systems.
... The scarcity of resources between pulses of water availability can limit plant growth (Cleverly et al., 2016), so that nutrient transfer between neighbouring plants may be crucial for species coexistence. Interplant nutrients transfer has also been studied in nonagronomic species under controlled conditions (Jalonen et al., 2009;Paula et al., 2015;Pickles et al., 2017;Teste et al., 2015;Wilson et al., 2006), and sometimes, even in the wild between co-occurring plants (Fernandez et al., 2020;He et al., 2006;Lerat et al., 2002;Montesinos-Navarro et al., 2016Simard et al., 1997;Teste et al., 2009), showing that it can happen in nature between certain pairs of species. However, despite its potential relevance, this process has been far less explored from a plant community perspective, assessing its role influencing plant community ecology. ...
... potential donors) was inserted in vials of 1.5 mL that were vertically attached to branches and afterwards sealed with playdough to reduce evaporation and avoid spillage. A solution of 2 g of urea enriched in 15 N (13CH₄15N₂O), 99 atom% 13 C, 98 atom% 15 N; Cambridge Isotope Laboratories, (Sercon Ltd.) and 1 mL of surfactant dissolved in 1 L of distillated water was prepared in the laboratory, and then 1 mL of solution was injected in each of the vials, letting the leaves immersed in this solution for 6 days (adapted from Montesinos-Navarro et al., 2016Putz et al., 2011). After 6 days of leaves immersion, labelled branches were cut to remove the vials without spillage. ...
Phenological segregation among species in a community is assumed to promote coexistence, as using resources at different times reduces competition. However, other unexplored nonalternative mechanisms can also result in a similar outcome. This study first tests whether plants can redistribute nitrogen (N) among them based on their nutritional temporal demand (i.e. phenology). Field ¹⁵N labelling experiments showed that ¹⁵N is transferred between neighbour plants, mainly from low N‐demand (late flowering species, not reproducing yet) to high N‐demand plants (early flowering species, currently flowering‐fruiting). This can reduce species' dependence on pulses of water availability, and avoid soil N loss through leaching, having relevant implications in the structuring of plant communities and ecosystem functioning. Considering that species phenological segregation is a pervasive pattern in plant communities, this can be a so far unnoticed, but widely spread, ecological process that can predict N fluxes among species in natural communities, and therefore impact our current understanding of community ecology and ecosystem functioning.
... Belowground facilitation occurs when one species makes previously unavailable P available to the other, due to the exudation of organic acids, phosphatases, or rhizosphere acidification resulting in increased P availability (Hinsinger et al. 2011). Since a decade ago, numerous studies have also pointed to the importance of soil-borne arbuscular mycorrhizal (AM) fungi of the phylum Glomeromycota (Tedersoo et al. 2020) in mediating inter-plant facilitation processes (van der Heijden et al. 2008;Montesinos-Navarro et al. 2016). In soils with strong Pi-fixing capacity, or where Pi is limiting, plant demand for this nutrient exceeds the rate at which it diffuses into the root zone, resulting in zones of Pi depletion surrounding the roots (Smith and Read 1997). ...
... The role of AM fungi in mixed plant communities is applicable due to their low host specificity: extra-radical hyphae can connect the roots of different plant species to form a common mycelial network (CMN) (Ingleby et al. 2007). This inter-plant mycorrhizal connection promotes facilitation through differential access to the nutrient pool from the common hyphal network and plant-to-plant nutrient transfers (Martins and Cruz 1998;Fitter et al. 1998;Leake et al. 2004;Hauggaard-Nielsen and Jensen 2005;van der Heijden and Horton 2009;Walder et al. 2012;Fellbaum et al. 2014;Gorzelak et al. 2015;Montesinos-Navarro et al. 2016). Remarkably, when associated to deep perennial tree roots, AM fungi increase the mycorrhiza-mediated uptake of soil nutrients, and thereby contribute to the nutrition of the co-cultivated species (Simard and Durall 2004;Ingleby et al. 2007;de Carvalho et al. 2010;Bainard, et al. 2011;Bainard et al. 2012). ...
Under agroforestry practices, inter-specific facilitation between tree rows and cultivated alleys occurs when plants increase the growth of their neighbours especially under nutrient limitation. Due to a coarse roots architecture limiting soil inorganic phosphate (Pi) uptake, walnut trees (Juglans spp.) exhibit dependency on soil-borne symbiotic arbuscular mycorrhizal fungi that extend extra-radical hyphae beyond the root Pi depletion zone. To investigate the benefits of mycorrhizal walnuts in alley cropping, we experimentally simulated an agroforestry system in which walnut rootstocks RX1 (J. regia x J. microcarpa) were connected or not by a common mycelial network (CMN) to maize plants grown under two contrasting Pi levels. Mycorrhizal colonization parameters showed that the inoculum reservoir formed by inoculated walnut donor saplings allowed the mycorrhization of maize recipient roots. Relative to non-mycorrhizal plants and whatever the Pi supply, CMN enabled walnut saplings to access maize Pi fertilization residues according to significant increases in biomass, stem diameter and expression of JrPHT1;1 and JrPHT1;2, two mycorrhiza-inducible phosphate transporter candidates here identified by phylogenic inference of orthologs. In the lowest Pi supply, stem height, leaf Pi concentration and biomass of RX1 were significantly higher than in non-mycorrhizal controls, showing that mycorrhizal connections between walnut and maize roots alleviated Pi deficiency in the mycorrhizal RX1 donor plant. Under Pi limitation, maize recipient plants also benefited from mycorrhization relative to controls, as inferred from larger stem diameter and height, biomass, leaf number, N content and Pi concentration. Mycorrhization-induced Pi uptake generated a higher carbon cost for donor walnut plants than for maize plants by increasing walnut plant photosynthesis to provide the AM fungus with carbon assimilate. Here we show for the first time that CMN alleviates Pi deficiency in co-cultivated walnut and maize plants, and may therefore contribute to limit the use of chemical P fertilizers in agroforestry systems.
... Generally, water stress appears to strongly inhibit N fixation and N facilitation in NFS (Bouillet et al. 2008;Ellsworth and Sternberg 2016), due to the constraints of plant physiology (Evans 1989;Richards et al. 2010), symbiotic bacteria, or mycorrhizal fungi (Hobbie and Högberg 2012). However, significant N fixation of NFS and interplant N facilitation between NFS and neighboring plants have been detected in desert communities (Montesinos-Navarro et al. 2016, and in water-and Nlimited estuarine wetlands where there is interplant competition for water sources (Wei et al. 2015). In addition to water use conditions, the growth demand of NFS and neighbor species should also be considered when analyzing the N fertilization effect (Forrester 2014;Husse et al. 2017;Taylor et al. 2017). ...
... The fixed N of NFS can be facilitated to neighboring plants directly through an interconnected hyphal network (He et al. 2005) or indirectly via litter decomposition or root exudates in soil (Paynel et al. 2001). Although the specific facilitation method was not examined in our study, the possible common mycorrhizal networks (CMNs) established between U. pumila and H. rhamnoides may allow direct N facilitation, because CMNs are effective networks for N transfer and likely occur in plant root AFM, through which mycelia can colonize neighboring roots (He et al. 2009;Hobbie and Högberg 2012;Montesinos-Navarro et al. 2016). Meanwhile, the significantly higher soil N content in PTHR and UPHR compared with the pure plantations of P. tabuliformis and U. pumila indicated a possible indirect facilitation pathway (Table S1). ...
Aims
Effects of water source relations on the facilitation of nitrogen (N) acquisition between N2-fixing species (NFS) and neighbor species require further investigation, especially in water- and N-limited conditions.
Methods
Plant water sources and leaf physiological parameters of Hippophae rhamnoides and two neighbor species were investigated in pure and mixed plantations. Then, N stable isotope and N content of leaves were analyzed to examine the N facilitation of H. rhamnoides to neighbor species. Finally, interactions between plant water sources and N acquisition were detected using the dissimilarity analysis.
Results
H. rhamnoides and Pinus tabuliformis obtained water from similar soil depths, whereas, water sources were partitioned between H. rhamnoides and Ulmus pumila. Compared with pure plantations, P. tabuliformis and H. rhamnoides could not maintain a stable net photosynthetic rate (Pn) during the dry period in mixed plantation. However, H. rhamnoides and U. pumila in mixed plantation could alleviate drought effect on Pn through stomatal adjustments, comapred with pure plantations. Furthermore, H. rhamnoides facilitated N to neighbor species regardless of their water source relations, however, this facilitation only significantly improved the leaf N content of U. pumila.
Conclusions
Water source partitioning, stomatal adjustment, and N facilitation promoted stable coexistence of NFS and neighbor species in water- and N-limited environments.
... The effects of mycorrhizal fungi on plant-plant interactions can be studied using different methods, both in the field and under controlled conditions. The presence of mycorrhizal fungi can be either enhanced through inoculation treatments, or reduced both physically, using meshes or digging trenches, and chemically with the application of fungicide to the soil (Ouahmane et al. 2006, Babikova et al. 2013, Zhang et al. 2014, Montesinos-Navarro et al. 2016a. Besides the inoculation of cultivated-fungal inoculums, mycorrhizal fungi can be indirectly enhanced by planting the facilitated species at increasing distances from the nurse (i.e. ...
... Our meta-analysis shows that most of the studies only consider increments in biomass and nutrient contents as potential benefits for facilitated plants. Only a few studies focus on how adult plants increase seedling survival through the transfer of nitrogen and carbon mediated by mycorrhizal fungi, the induction volatiles' production to avoid herbivore-insects or the enhancement of nutrient transfer among adult plants promoting long-lasting facilitative interactions (Teste et al. 2009, Babikova et al. 2013, Song et al. 2015, Montesinos-Navarro et al. 2016a). This suggests a gap of knowledge regarding these other potential ways by which mycorrhizal fungi benefit plant facilitative interactions. ...
The diversity of pathways through which mycorrhizal fungi alter plant coexistence hinders the understanding of their effects on plant‐plant interactions. The outcome of plant facilitative interactions can be indirectly affected by mycorrhizal symbiosis, ultimately shaping biodiversity patterns. We tested whether mycorrhizal symbiosis enhances plant facilitative interactions and whether its effect is consistent across different methodological approaches and biological scenarios. We conducted a meta‐analysis of 215 cases (involving 21 nurse and 29 facilitated species), in which the performance of a facilitated plant species is measured in the presence or absence of mycorrhizal fungi. We show that mycorrhizal fungi significantly enhance plant facilitative interactions mainly through an increment in plant biomass (aboveground) and nutrient content, although their effects differ across biological contexts. In semiarid environments mycorrhizal symbiosis enhances plant facilitation, while its effect is non‐significant in temperate ecosystems. In addition, arbuscular but not ecto‐mycorrhizal (EMF) fungi significantly enhances plant facilitation, particularly increasing the P content of the plants more than EMF. Some knowledge gaps regarding the importance of this phenomenon have been detected in this meta‐analysis. The effect of mycorrhizal symbiosis on plant facilitation has rarely been assessed in other ecosystems different from semiarid and temperate forests, and rarely considering other fungal benefits provided to plants besides nutrients. Finally, we are still far from understanding the effects of the whole fungal community on plant‐plant interactions, and on plant species coexistence.
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... There is evidence that facilitative interactions drive a patchy vegetation distribution of the vegetation in this environment (Valiente-Banuet and Verdú 2007, 2008, Castillo et al. 2010, Verdú and Valiente-Banuet 2011. Within these vegetation patches, recent studies have shown that the nurse plant can transfer N to different species of facilitated plants through common mycorrhizal networks (Montesinos-Navarro et al. 2016). ...
... Finally, we consider it unlikely that the observed pattern is driven by interspecific differences in the natural rates of leaf 15 N accumulation. We showed previously in a simultaneous experiment similarly measuring 15 N transfer from nurse plants to their facilitated species (Montesinos-Navarro et al. 2016), that leaf δ 15 N enrichment across facilitated plant species was significantly reduced when soil fungal abundance was reduced using a fungicide. This implies that the leaf δ 15 N enrichment observed in facilitated plants was due to actual 15 N tracer transfer from the nurse plants, and not driven by interspecific differences in the rates of natural 15 N accumulation. ...
Plant facilitative interactions enhance co-occurrence between distant relatives, partly due to limited overlap in resource requirements. We propose a different mechanism for the coexistence of distant relatives based on positive interactions of nutrient sharing. Nutrients move between plants following source-sink gradients driven by plant traits that allow these gradients to establish. Specifically, nitrogen (N) concentration gradients can arise from variation in leaf N content across plants species. As many ecologically relevant traits, we hypothesize that leaf N content is phylogenetically conserved and can result in N gradients promoting N transfer among distant relatives. In a Mexican desert community governed by facilitation, we labelled nurse plants (Mimosa luisiana) with (15) N and measured its transfer to 14 other species in the community, spanning the range of phylogenetic distances to the nurse plant. Nurses established steeper N source-sink gradients with distant relatives, increasing (15) N transfer towards these species. Nutrient sharing may provide long-term benefits to facilitated plants and may be an overlooked mechanism maintaining coexistence and increasing the phylogenetic diversity of plant communities. This article is protected by copyright. All rights reserved.
... Under nurse species, including O. tesota, the microenvironment is more benign, with greater soil fertility associated with the accumulation of nutrients such as organic matter, nitrogen, and potassium (Suzán et al. 1996. The higher fertility and better soil properties under nurse plants have been linked to the abundance of AMF, owing to their role in soil formation and stabilization, their capacity to acquire and exchange nitrogen (N), phosphorus (P), and water, thereby enhancing the performance of the facilitated species (Carrillo-García et al. 1999, Montesinos-Navarro et al. 2016, Sortibrán et al. 2018. ...
Background: Columnar cacti survival in deserts occurs mainly under nurse plants, due to better conditions for germination and establishment, as greater humidity, and nutrient concentration. However, interactions like the association between arbuscular mycorrhizal fungi (AMF) and roots remain relatively unexplored. We evaluated the mycorrhizal status and soil rhizosphere properties of four columnar cacti species growing both under and outside their nurse plant. Hypotheses: Soil properties improvement under nurse plants has been correlated with the abundance of AMF. Therefore, a greater number of AMF structures and roots mycorrhization would be in facilitated plants, compared to the same species growing outside the nurse. Studied species: Nurse plant: Olneya tesota, facilitated species: Carnegiea gigantea, Pachycereus pringlei, Pachycereus schottii, and Stenocereus thurberi. Study site and dates: Central Gulf Coast subdivision of the Sonoran Desert, Sonora, Mexico. Methods: Cacti roots and soil rhizosphere were collected under and outside the nurse plant. Roots were stained, and mycorrhizal colonization (MC), hairy roots (HR), visual density (VD), and number of spores were determined. Physicochemical soil properties were analyzed. Results: Values of MC, VD, spore number, organic matter (OM), nitrate, and total and assimilable phosphorous were higher under the nurse compared to bare areas. Conclusions: The hypothesis that mycorrhization parameters are greater in roots of cacti growing under the nurse was confirmed, besides previous knowledge about soil quality under nurse plants, suggesting that AMF play a significant role in the cacti facilitation process under nurses plants, and that nurse plant plays a significant role in AMF formation.
... Under nurse species, including O. tesota, the microenvironment is more benign, with greater soil fertility associated with the accumulation of nutrients such as organic matter, nitrogen, and potassium (Suzán et al. 1996. The higher fertility and better soil properties under nurse plants have been linked to the abundance of AMF, owing to their role in soil formation and stabilization, their capacity to acquire and exchange nitrogen (N), phosphorus (P), and water, thereby enhancing the performance of the facilitated species (Carrillo-García et al. 1999, Montesinos-Navarro et al. 2016, Sortibrán et al. 2018. ...
Se describe el estado micorrícico y propiedades del suelo rizosférico de cuatro especies de cactus columnares creciendo tanto debajo como fuera de su nodriza Olneya tesota, ya que se ha relacionado el mejoramiento de propiedades del suelo bajo la nodriza con la abundancia de HMA.
... Algunas especies de Mimosa son elementos florísticos que potencian la restauración de sus ambientes (Camargo-Ricalde et al. 2002, Montaño-Arias et al. 2015, 2018 (Chimal-Sánchez et al. 2016 y una alta dependencia micorrízica que, en conjunto con las bacterias nodulantes, favorecen su propio crecimiento (Camargo-Ricalde et al. 2010a). Lo anterior, podría regular la circulación de nutrientes entre plantas, particularmente con aquellas que son filogenéticamente distantes (Montesinos-Navarro et al. 2016). Sin embargo, el conocimiento sobre el crecimiento de las especies de Mimosa, la asignación de biomasa y los efectos que tienen los HMA y las bacterias fijadoras de N 2 sobre estas variables es escaso (Camargo-Ricalde et al. 2010a, Montaño-Arias et al. 2021. ...
Antecedentes: En plantas, las compensaciones morfo-fisiológicas, así como las asociaciones microbianas, regulan el uso de recursos limitantes y el ensamblaje de las comunidades vegetales.
Pregunta: ¿Qué relación tienen la micorrización arbuscular y nodulación bacteriana en el crecimiento y asignación de biomasa de ocho especies de Mimosa?
Especies de estudio: Mimosa adenantheroides, M. biuncifera, M. calcicola, M. lacerata, M. luisana, M. polyantha, M. purpusii y M. texana var. filipes.
Sitio de estudio y fechas: Valle de Tehuacán-Cuicatlán, Puebla-Oaxaca, México, 2013 y 2014.
Método: Las plantas crecieron en dos tratamientos: i) Con inóculo de hongos micorrizógenos arbusculares (HMA) y bacterias fijadoras de N2 (BFN) de islas de recursos (IR) de Mimosa y ii) sin inóculo, con nueve réplicas por especie/tratamiento. Se evaluó el crecimiento de las plantas, la micorrización arbuscular y la nodulación en las raíces.
Resultados: Las especies de Mimosa, creciendo sin inóculo, variaron en crecimiento y asignación de biomasa con valores inferiores al tratamiento con inóculo, y se agruparon en tres diseños morfológicos: i) M. calcicola y M. lacerata; ii) M. adenantheroides, M. luisana y M. polyantha; y iii) M. biuncifera, M. purpusii y M. texana var. filipes. Asimismo, las ocho especies conformaron un cuarto diseño cuando crecieron con inóculo que favoreció su crecimiento y modificó sus patrones de asignación de biomasa.
Conclusiones: Los resultados contribuyen a delinear posibles grupos funcionales en Mimosa, pero se requiere la evaluación de otros rasgos funcionales para seleccionar especies con potencial en la restauración ambiental y comprender el ensamblaje de las comunidades vegetales.
... The key mechanism underpinning AMF's influences on N transfer is that they can establish reciprocal symbionts with neighboring plant roots (Nanjareddy et al., 2014), and the external hyphae of symbionts can form a wide range of common mycorrhizal network (CMN) in soil (Bucking et al., 2016). N can be transported directly from legumes to non-legume plants by this CMN (Montesinos-Navarro et al., 2016). This AMF-mediated N transfer is largely driven by the source-sink relationship between plants (i.e., transferring from plants with high N concentration to plants with low N concentration), which reduces energy consumption (Jalonen et al., 2009;Muneer et al., 2020). ...
In maize-soybean intercropping systems, the transfer of N from soybean to maize gives the intercropping system the advantage of improved N utilization and higher yields. Mycorrhiza acts as an important pathway for N transfer, providing a constant supply of N to sustain the growth and development of maize in its early stages. However, it is not clear how arbuscular mycorrhizal fungi (AMF) drive the transfer of N from soybean to maize in the intercropping system. Therefore, we quantified the amount of N transferred from soybean to maize under low and high N levels in the intercropping system, and the abundance and diversity of AMF involved in N transfer (15N-AMF) under different conditions by 15N leaf marker and DNA-SIP technology. We found that the interaction between roots and reducing the application of N fertilizer increased the amount of N transfer from soybean to maize. Compared with plastic plate separation (PS), no separation (NS) and mesh separation (MS) significantly increased the N fixation rate (from 14.33% to 39.09%), and the amount of N transfer under NS was 1.95–3.48 times that under MS. N transfer from soybean to maize ranged from 9.7 to 43.42 mg per pot in the no N treatment, while the addition of N fertilizer reduced N transfer by 14.12–66.28%. This is due to root interaction and reduced N fertilization increased the abundance and diversity of the 15N-AMF community, thereby promoting AMF colonization of maize and soybean roots. AMF colonization in soybean and maize roots under NS treatment was 6.47–17.24% higher than under MS treatment in all three levels of N addition. The increase of mycorrhiza in root system increased the N transfer from soybean to maize significantly. These results suggest that reduced N fertilizer in maize-soybean intercropping systems can increase N transfer by the mycorrhizal pathway, meeting maize N requirements and reducing chemical N fertilizer, which is important for sustainable agricultural development.
... Nitrogen transfer was relatively high (4% of the donor plant N) among these non-N 2fixation plants with contrasting N-acquisition strategies. Montesinos-Navarro et al. (2016) found that CAMNs mediated N transfer between facilitated plants, suggesting that nutrient transfer through CAMNs might be a potential mechanism allowing persistent benefits for their adult facilitated plants. The potential pathways for CAMNs-mediated N transfer could be (1) direct transfer of N via connecting hyphae across the symbiotic interface, (2) increased root surface area and a reduced distance for nutrient diffusion, and (3) increased assimilation or exudation of N in the AM-colonized plants (Haystead et al., 1988;Trannin et al., 2000;He et al., 2003;He et al., 2009). ...
Arbuscular mycorrhizal fungi (AMF) are ubiquitous in soil and form nutritional symbioses with ~80% of vascular plant species, which significantly impact global carbon (C) and nitrogen (N) biogeochemical cycles. Roots of plant individuals are interconnected by AMF hyphae to form common AM networks (CAMNs), which provide pathways for the transfer of C and N from one plant to another, promoting plant coexistence and biodiversity. Despite that stable isotope methodologies (¹³C, ¹⁴C and ¹⁵N tracer techniques) have demonstrated CAMNs are an important pathway for the translocation of both C and N, the functioning of CAMNs in ecosystem C and N dynamics remains equivocal. This review systematically synthesizes both laboratory and field evidence in interplant C and N transfer through CAMNs generated through stable isotope methodologies and highlights perspectives on the system functionality of CAMNs with implications for plant coexistence, species diversity and community stability. One-way transfers from donor to recipient plants of 0.02-41% C and 0.04-80% N of recipient C and N have been observed, with the reverse fluxes generally less than 15% of donor C and N. Interplant C and N transfers have practical implications for plant performance, coexistence and biodiversity in both resource-limited and resource-unlimited habitats. Resource competition among coexisting individuals of the same or different species is undoubtedly modified by such C and N transfers. Studying interplant variability in these transfers with ¹³C and ¹⁵N tracer application and natural abundance measurements could address the eco physiological significance of such CAMNs in sustainable agricultural and natural ecosystems.
... Since legumes usually depend much less on soil N than non-leguminous species, they face less competition with neighboring plants and can even have facilitative effects on these . Direct facilitation occurs when non-legumes directly benefit from N transferred via mycorrhiza from legumes (Frey and Schüepp 1993;Montesinos-Navarro et al. 2016). In contrast, we here refer to indirect facilitative effects when neighboring species have additional soil N available as legumes use atmospheric N instead (Bessler et al. 2012). ...
Facilitation has been a long-neglected type of interaction but received more attention recently. Legumes are commonly involved in facilitative interactions due to their nitrogen fixation. Facilitative interactions are so far underappreciated yet potentially important for biological invasions, especially given increasing numbers of alien species. In a common garden experiment using 30 annual Asteraceae species (neophytes, archaeophytes, plus some natives), grown in communities with or without legume presence, we measured functional traits and fitness in focal Asteraceae, as well as nitrogen characteristics of Asteraceae and two native community phytometer species. We investigated how legume presence affects relationships between trait and nitrogen concentration and Asteraceae fitness; and whether mechanisms of facilitation in legume presence and its effects on aboveground performance differ among native phytometer, neophyte, and archaeophyte Asteraceae using the δ ¹⁵ N natural abundance method. Lower specific leaf area was associated with higher aboveground biomass and seed production, with a stronger effect in legume absence. Nitrogen concentration had a positive relationship with biomass, but did not generally increase seed production. Our results hint at N facilitation for the native grass phytometer Festuca rupicola when growing in legume presence, whereas the forb Potentilla argentea and 27 alien Asteraceae species did not indicate facilitative effects. Intriguingly, direct legume facilitation in native phytometer species was only detected when growing with archaeophytes neighbors, not with neophytes. This hints at varied mechanisms of competition for nitrogen between natives and alien species of different residence time and deepens the understanding of altered facilitative leguminous effects in alien species presence.
... (Montesinos-Navarro et al. 2012), supply nutrients such as nitrogen and phosphorous, and the connection of roots through hyphae of different species, enabling a selective nutrient transference between them(Montesinos-Navarro et al. 2016, 2017. This indicates that in the facilitation process, besides the modification of the physical microenvironmental beneath plant canopies, microbiome-plant interaction networks play an outstanding role. ...
... Inicialmente se consideró un alto nivel de especificidad en la simbiosis micorrízica. En la actualidad se conoce que las hifas de ma conectan las raíces de plantas de diferentes especies, lo cual favorece la transferencia de nutrientes entre ellas (Montesinos-Navarro et al., 2016), incluso pueden aportar más nitrógeno a otros individuos y retener menos cantidad (Montesinos-Navarro et al., 2017). Además del microambiente rizosférico bajo el dosel, se forman redes de interacción microbioma-planta con alto potencial de especificidad, que pueden establecer reconexiones ante la ausencia de las especies con mayor afinidad y contrarrestar la cascada de extinción vegetal en áreas fragmentadas (Montesinos-Navarro et al., 2019). ...
Esta obra presenta el conocimiento generado sobre la biología, ecología y biotecnología del complejo Agave angustifolia, con la participación interdisciplinaria e interinstitucional de investigadores. Brinda a los productores una opción de manejo sostenible del agave con un aprovechamiento diversificado e integral. La micropropagación puede generar las cantidades requeridas de plantas para cultivos, forestación y/o recuperación de poblaciones silvestres. Para el trasplante en áreas naturales se valida un modelo holístico con base en los factores bióticos y abióticos del sitio. Esta alternativa biotecnológica es viable, por el costo razonable de las vitroplantas, el porcentaje de prendimiento alto y el manejo 100 % orgánico sin riegos, fertilizantes ni plaguicidas. Se promueve el uso del agave como fuente de fibra a través de la biomasa foliar, el bagazo del tallo para la generación de bioenergía, los fructanos en prebióticos de humanos y animales, y el rescate del conocimiento ancestral como alimento y medicinal. Elementos esenciales Describe una alternativa biotecnológica para el manejo sostenible del agave a través de la micropropagación y el trasplante holístico en áreas naturales Restablece y circunscribe Agave pacifica para Sonora Explica los estudios citogenéticos y de variabilidad génica en poblaciones silvestres Esclarece la importancia de las plantas nodrizas y los hongos promotores de crecimiento en el establecimiento exitoso del agave Destaca la aplicación de la calorespirometría como un método de selección temprana de agaves altamente productivos Coedición con Editorial Fontamara, S.A. de C.V.
... In general, the high variability in the literature may reflect many different factors that might interfere in plant-to-plant interaction, such as differences in environmental conditions, in the different experimental setups, or plant and fungi combinations, soil nutrient supply, additional stress conditions added (e.g., nutrients deficiency, drought, shading, etc.), and the general experimental design (e.g., field, pot or microcosmos experiments). In addition, like for C, quantification of N transfer via interconnecting hyphae is not distinguishable from other pathways (Montesinos-Navarro et al., 2016;Fang et al., 2021). The distinction and relative importance of the different pathways determines the strength, direction, and outcome of interactions among plants and soil organisms, requiring new technologies and ideas to address such issues. ...
Most terrestrial plants establish symbiotic associations with mycorrhizal fungi for accessing essential plant nutrients. Mycorrhizal fungi have been frequently reported to interconnect plants via a common mycelial network (CMN), in which nutrients and signaling compounds can be exchanged between the connected plants. Several studies have been performed to demonstrate the potential effects of the CMN mediating resource transfer and its importance for plant fitness. Due to several contrasting results, different theories have been developed to predict benefits or disadvantages for host plants involved in the network and how it might affect plant communities. However, the importance of the mycelium connections for resources translocation compared to other indirect pathways, such as leakage of fungi hyphae and subsequent uptake by neighboring plant roots, is hard to distinguish and quantify. If resources can be translocated via mycelial connections in significant amounts that could affect plant fitness, it would represent an important tactic for plants coexistence and it could shape community composition and dynamics. Here, we report and critically discuss the most recent findings on studies aiming to evaluate and quantify resources translocation between plants sharing a CMN and predict the pattern that drives the movement of such resources into the CMN. We aim to point gaps and define open questions to guide upcoming studies in the area for a prospect better understanding of possible plant-to-plant interactions via CMN and its effect in shaping plants communities. We also propose new experiment setups and technologies that could be used to improve previous experiments. For example, the use of mutant lines plants with manipulation of genes involved in the symbiotic associations, coupled with labeling techniques to track resources translocation between connected plants, could provide a more accurate idea about resource allocation and plant physiological responses that are truly accountable to CMN.
... In addition, the fungal mycelia simultaneously colonize and interconnect roots of the same or different plant species, forming so-called common mycorrhizal networks (CMNs). The CMNs allow direct and efficient pathways of resource transfers between intercrops, and closely bound to the outcomes of plant facilitative or competitive interactions (Montesinos-Navarro et al., 2016;Qiao et al., 2016;Dieng et al., 2017). Furthermore, AM fungi can provide a bunch of services for plant adaptation under stressful environments (Gorzelak et al., 2015), facilitating the ecological functions and wider applications of intercropping (Ehrmann and Ritz, 2014). ...
Intercropping, which gains productivity and ecological benefits through plant facilitative interactions, is a practice often associated with sustainable agriculture. In such systems, arbuscular mycorrhizal (AM) fungi and the hyphal networks play key roles in plant facilitation by promoting connectivity, mediating interplant transfer of metabolic resources, and managing weeds, pathogens, and contaminants. This review states that the symmetrically or unsymmetrically delivered resources via AM fungi are imperative to maintain facilitative interactions between intercrops. In addition, the responses of AM fungi to intercropping are also discussed, including changes in abundance, diversity, community composition and colonization level. Although general proliferations in AM fungi via intercropping have been shown, the plant hosts and neighbors may exert different influences on AM fungi. Therefore, further research is needed in quantifying the mediating role of AM fungi on outputs of intercropping systems, clarifying the driving forces, and exploring the causation between these processes and the changes in AM fungi themselves. To conclude, the integration with AM fungi extends the understanding of key soil biological processes driving plant facilitation and will guide efforts to optimizing intercropping systems.
... The importance of this type of association is clear for several cacti species, which benefit during their earliest life stages from the enhanced microhabitat conditions beneath the canopy of shrubs from the families Fabaceae, Asteraceae, Mimosaceae, and Asparagaceae (Nobel 1984;Franco and Nobel 1989;Mandujano et al. 2001;Rojas-Sandoval and Meléndez-Ackerman 2012). The microhabitat created by nurse plants protects seedlings by reducing the total daily photosynthetically active radiation (PAR) (Franco and Nobel 1989), decreases the maximum soil surface temperature (Nobel 1980;Franco and Nobel 1989;Munguía-Rosas and Sosa 2008;Miranda-Jácome et al. 2013), reduces evapotranspiration , improves soil properties (Munguía-Rosas and Sosa 2008;Montesinos-Navarro et al. 2016), and protects seeds and seedlings from predation (Mcauliffe 1984;Sosa and Fleming 2002;Holland and Molina-Freaner 2012). ...
Seeds and seedlings are the most critical stages of cacti life cycles. From the thousands of seeds produced in a reproductive season, only a small fraction successfully germinate, the rest are lost to predation, go dormant, and remain viable in the seed bank, or lose viability. These early stages often depend on facilitation by nurse plants for germination and seedling recruitment. We aim to prescribe actions for the conservation of Cephalocereus polylophus by improving recruitment in the population. The viability of seeds with different storage times was evaluated as an indicator of their potential to form a short-term seed bank. Through the analysis of seed germination and seedling survival under the canopy of two nurse plant species and open areas, we assessed the importance of facilitation for recruitment. A predator exclusion experiment evaluated the intensity of granivory and herbivory on seedlings of different ages. Seeds had germination rates above 90% under laboratory conditions , even after 2 years of storage. Seed germination was only registered under one of the two nurses and after 2 years, up to 4% of the seedlings planted under both nurse plants survived. Age and protection against herbivores increased seedlings survival. Facilitation and age are crucial for the recruitment of C. polylophus, and future conservation programs should include the protection of plant communities and the introduction of seedlings instead of seeds.
... Mimosa species, and a wide range of plants associated to them, are favored in biomass and nutrients through AMF in the RI Camargo-Ricalde et al., 2010a;Montesinos-Navarro et al., 2016;Sorbitrán et al., 2019). Biocrusts composed of mosses, lichens, cyanobacteria, fungi, green algae and soil particles are present inside and outside M. luisana-RI (Rivera-Aguilar et al., 2006;Sandoval-Pérez et al., 2016). ...
Background:
Arbuscular mycorrhizal fungi (AMF) and biocrusts (BC), occur inside and outside Mimosa luisana resource islands (M. luisana-RI) at the Tehuacán-Cuicatlán Valley, Puebla-Oaxaca, Mexico.
Objectives:
To determine: 1) Whether there are AMF within biocrusts, 2) The abundance and richness of AMF, and 3) The potential of AMF propagation in BC and soil below BC inside (BC-RI, soil-BC-RI) and outside (BC-ORI, soil-BC-ORI) M. luisana-RI, and open areas (OA), in the rainy (September 2011) and dry (May 2012) seasons.
Methods:
AMF were extracted of biocrusts and soil samples collected inside and outside M. luisana-RI and OA, in both seasons. Spore abundance and species richness, as well as potential propagation of AMF were determined in laboratory and greenhouse.
Results and Conclusions:
Biocrusts inside and outside M. luisana-RI form reservoirs of AMF spores and species richness (12 spp.), and act as “shields” protecting AMF compared with OA (5 spp.). Seasonal changes in the AMF composition within the biocrusts and the soil suggest that the availability of water drives AMF assemblages. The AM fungal spores in BC-RI and BC-ORI have a high potential of propagation; however, the BC-ORI by buffering the loss of AMF in soil-BC-ORI, they form mycorrhizal inocula within the soil.
... However, despite marked variability in the x( 15 N) of fine roots between labelled acacias, the use of Equation (3) based on the relative differences in x( 15 N) between fine roots of a given Acacia tree and Eucalyptus neighbours made it possible to reliably estimate the effect of nutrient deficiency on the belowground transfer of N. Short-term belowground N transfer may occur directly via common mycorrhizal networks (CMNs) (Simard and Durall, 2004;Selosse et al., 2006;He et al., 2019) or root exudates of N compounds (Marschner and Dell, 1994;Fustec et al., 2010), or indirectly through rapid decomposition of very fine roots and microbial tissues (May and Attiwill, 2003;Staddon et al., 2003). Montesinos-Navarro et al. (2016) showed that short-term belowground N transfer between adult plants can be more effective by CMNs than via root exudates. CMNs can be formed by arbuscular mycorrhizal fungi (AMF) (Montesinos-Navarro et al., 2012) or ectomycorrhizal fungi (He et al., 2005). ...
While a recent study showed that significant amounts of the nitrogen (N) requirements of young Eucalyptus trees can be provided by nitrogen-fixing trees (NFTs) in mixed-species plantations through short-term belowground N transfer, the consequences of soil fertility on this facilitation process remain unknown. We assessed the effect of fertilization on the percentage of N derived from transfer (%NDFT) from Acacia mangium trees to Eucalyptus trees in mixed-species plantations. A complete randomized block design with two treatments (fertilized vs unfertil-ized) and three blocks was set up in mixed-species plantations of A. mangium and Eucalyptus in Brazil, with 50% of each species at 2.5 m × 2.5 m spacing. Collection of litterfall and forest floor made it possible to estimate the annual N release from forest floor decomposition between 46 and 58 months after planting, close to harvest age. 15 N-NO 3-was injected into the stem of one dominant Acacia tree in each plot, 58 months after planting. The x (15 N) values of Acacia and Eucalyptus fine roots sampled within 1.8 m of the labelled A. mangium tree were determined at 7, 14, 30 and 60 days after labelling. The x(15 N) values in wood, bark, branch and leaf samples were also determined for the 6 labelled Acacia trees and their two closest Eucalyptus neighbours, just before and 60 days after labelling. The amount of N released from forest floor decomposition was 31% higher in fertilized (F+) than in unfertilized (F-) plots. Sixty days after labelling, the aboveground compartments of Eucalyptus trees were significantly 15 N enriched in both treatments. The x(15 N) values of Acacia fine roots were higher than background values from 7 days after labelling onwards in F+ and 30 days after labelling in F-. The x(15 N) values of Eucalyptus fine roots were higher than background values in both treatments, from 30 days after labelling onwards. Mean %NDFT values were 18.0% in F+ and 33.9% in F-over the first 60 days after labelling, and 22.8% in F+ and 67.7% in F-from 30 to 60 days after labelling. Fertilization decreased short-term transfer belowground of N from Acacia trees to Eucalyptus trees. Our study suggests that belowground facilitation processes providing N from NFTs to Eucalyptus trees in mixed-species plantations are more pronounced in low-fertility soils than in nutrient-supplied stands.
... But, again, despite the rationale was that persistent interactions would be those involving the most functionally different species, phenotypically informed networks have never been used to test this hypothesis. Increasing evidence on the permanence of interactions between functionally different species exist (Navarro-Cano et al., 2019), and explanations have invoked not only the conventional wisdom of competition reduction but also mutual help between species (Sortibr an et al., 2014(Sortibr an et al., , 2019Montesinos-Navarro et al., 2016. These new results open a research avenue to search for functional traits that could be putatively involved in the maintenance of facilitation networks with time. ...
Identifying the plant traits that determine the outcome of facilitation interactions is essential to understand how communities are assembled and can be restored. Plant facilitation networks are phylogenetically structured but which traits are behind such a pattern is unknown. We sampled plant interactions in stressful ecosystems from south‐eastern Spain to build seedling and adult facilitation networks. We collected 20 morphological and ecophysiological traits for 151 species involved in interactions between 879 nurse individuals benefiting 24 584 seedlings and adults. We detected a significant phenotypic signal in the seedling facilitation network that was maintained in the adult network, whereby functionally similar nurses tended to facilitate functionally similar species whose traits differ from those of their nurses. We provide empirical evidence to support a long‐lasting theoretical postulate stating that facilitation networks are phenotypically structured. Trait matching through which nurse and facilitated species avoid phenotypic overlap, and consequently competition, is the main linkage rule shaping plant facilitation networks.
... Firstly, a short 14-day time of 15 N transfer must be considered. Similar N transfer results (%NDFT was 2.64%) were observed after 15 days of 15 N labeling [51]. Several studies showed that %NDFT could be up to 40% of total N in the facilitated plant over several months [24,52,53]. ...
Few studies have examined if perennial leguminous cover crops are able to transfer nitrogen (N) via common mycorrhizal networks (CMNs) to neighboring fruit trees; the gradient of such N transfer could affect the N nutrition of both plants. Using separated three-column chambers to grow plants in a greenhouse, 99 atom% 15 N as (15 NH4)2SO4 was applied to leaves of white clover (Trifolium repens L.) and 15 N was then traced in neighboring citrus (Citrus sinensis (L.) Osbeck) seedlings interconnected by an arbuscular mycorrhizal fungus (AMF, Rhizophagus intraradices). A range of 66.85-68.74% mycorrhizal colonization in white clover (mycorrhizal and/or Rhizobium trifolii in-oculated) and 19.29-23.41% in citrus (non-mycorrhizal inoculated) was observed after 12 months of AMF inoculation in the white clover, indicating a successful CMN linkage was established between these two plant species. This CMN establishment resulted in significant increases in biomass, N accumulation, and 15 N content of citrus when accompanied with nodulated and mycorrhizal fungus colonized white clover. N transfer from white clover to citrus was significantly greater under nod-ulation plus mycorrhization (46.23 mg N per pot, 1.71% of N transferred) than under non-inoculated control (4.36 mg N per pot, 0.21% of N transferred), and higher than sole mycorrhization (36.34 mg N per pot, 1.42% of N transferred). The percentage of N in citrus derived from white clover under nodulated/mycorrhization was 1.83-1.93%, and was highest in leaves (3.31%), moderate in stems (2.47%), and lowest in roots (0.41%) of citrus. In summary, results from this experiment demonstrated that nearly 2.0% of N transferred from white clover to citrus via CMN. Further studies are needed to quantify N transfer between white clover and citrus by other routes, including soil or root exudation pathways.
... The role of these fungi in mixed plant communities is amplified by their low host specificity, so that extra-radical hyphae connect the roots of different plant species to form a common mycelial network (CMN). CMNs linking co-cultivated plant species can mediate facilitation via nutrient transfer (Martins and Cruz 1998;Fitter et al. 1998;He et al. 2003;Leake et al. 2004;Hauggaard-Nielsen and Jensen 2005;van der Heijden and Horton 2009;Walder et al. 2012;Fellbaum et al., 2014;Gorzelak et al. 2015;Montesinos-Navarro et al. 2016), but also interference competition by releasing allelopathic chemicals that directly inhibit growth (Barto et al. 2012;Salahuddin et al. 2018). Understanding positive and negative feedbacks between mixed walnut plantations and AM fungi is therefore of critical importance in the management of mixed cropping systems. ...
Walnut trees are among the most important hardwood species in the northern hemisphere, ecologically and economically. They are mainly cultivated for timber and nut production but are also attractive ornamental trees in parks. Establishing walnut orchards is difficult because seedlings have a coarse root architecture and few of them survive to transplanting. Planting success is mainly determined by the root system morphology and the nutrient status of the seedlings, so that rhizosphere conditions are critical for plant performance. Walnut trees can associate with soil-borne arbuscular mycorrhizal fungi, which are obligate biotrophs. In this association, plant-produced carbon compounds are traded against fungus-acquired soil mineral nutrients. The beneficial effect of arbuscular mycorrhizal symbiosis on hardwood seedling quality and field performance has long been known, but an integrated view is lacking about the effects of arbuscular mycorrhizas on walnut cropping. Therefore, we surveyed the literature published over the last 40 years to provide up-to-date knowledge on the relationships between arbuscular mycorrhizas and walnut trees. Our review outlines the major following points: (1) the arbuscular-mycorrhiza-mediated nutrient uptake capacity of walnut trees is associated with first- to third-order roots, and fibrous tip-ended roots are dependent on arbuscular mycorrhizal fungi, whereas pioneer roots are not; (2) early inoculation with arbuscular mycorrhizal fungi improves the survival and seedling performance attributes of transplanted walnut trees: biotization enhances walnut transplant success by increasing the number of lateral roots and plant P uptake, but these benefits are fungus- and host-dependent; (3) in the context of walnut agroforestry, deeply rooted walnut trees play a role as reservoirs of arbuscular mycorrhizal fungal propagules for the surrounding vegetation, but tree shade and soluble phosphate availability decrease walnut mycorrhizal dependency; and (4) the arbuscular mycorrhizal mycelium mediates the transport of juglone and thus plays a role in walnut tree allelopathy.
... In the same 1949 line, compartmental modelling based on testing different pathways of N transfer may help 1950identify and rank these fluxes. Our results also suggest that mycorrhizae may be key players in 1951 N transfer as previous studies mentioned it(Montesinos-Navarro et al. 2016, 2019b). 1952 Interference between oak and Molinia might result in quantitative and/or qualitative changes in 1953 mycorrhizal communities in both oak and/or Molinia roots. ...
A better understanding of plant interactions would improve the management of natural and artificial forest regeneration. It is well established that Molinia (Molinia caerulea), a monopolist species of understory, has a particularly depressive effect on young sessile oak (Quercus petraea) establishment and growth. Large capacity of Molinia in water and soil nutrients uptake leads to strong competition by resources exploitation. However, it seems that other interactions are involved in the relationship between young oak and Molinia. Thus, the allelopathic properties of Molinia have been suggested, but no study has shown such an effect on oak. Inversely, young oak seems to facilitate Molinia growth. Oak-Molinia interaction thus has the singularity of being antagonistic: the Molinia inhibits oak growth while this one favors grass growth, but the mechanisms involved are not entirely known. The aim of this thesis was to analyze the functional and ecophysiological mechanisms involved in the interactions between young sessile oak and Molinia. The experiments carried out in the thesis show that (i) oak quickly transfers nitrogen to Molinia by the underground pathways (rhizodeposition of nitrogen compounds in the soil) favoring grass growth, (ii) Molinia presence in the same pot leads to a decrease in the lateral root rate and ectomycorhization rate of oak and (iii) Molinia rhizodeposes secondary metabolites different from those of oak and have an allelopathic potential. In line with current work, the thesis puts into perspective that the chemical compounds emitted by plants in the soil act as real direct or indirect signals (via the biological communities of the soil) and induce neighbors modifications in their metabolism and / or their growth.
... This mycorrhizal association facilitates nutrient uptake from the soil via extraradical mycelia, improving growth and fitness of the host plant and, at the same time, the fungal partner receives essential carbohydrates (Smith and Read 2008) and lipids (Keymer et al. 2017). Also, AMF have a wide functional diversity that positively impacts on cycling of nutrients, the formation of stable aggregates into the soil (Rillig 2004;Chaudhary et al. 2009), the persistence of plant-plant facilitative interactions (Montesinos-Navarro et al. 2016), and plant diversity and productivity, among other important roles in terrestrial ecosystems (Van der Heijden et al. 2008;Powell and Rillig 2018). ...
Septoglomus mexicanum is here described as a new species of arbuscular mycorrhizal fungi (AMF; Glomeromycota) based on morphological and phylogenetic analyses. It was isolated from rhizospheric soil of two endemic Mexican legumes: Prosopis laevigata and Mimosa luisana, which grow in semiarid regions of central Mexico. Septoglomus mexicanum is characterized by forming globose spores of (154.5–)202.8(–228.9) µm diam and a spore wall consisting of four layers (SWL1–SWL4): outer wall layer (SWL1) hyaline, evanescent, (1.7–)3.2(–4.3) µm thick; SWL2 laminate and smooth, orange to reddish orange, (3.1–)4.5(–6.1) µm thick; SWL3 laminate, smooth, reddish orange to reddish brown, (4.1–)5.1(–5.7) µm thick; and SWL4 hyaline, semiflexible, (0.93–)1.2(–1.4) µm thick. None of the spore wall layers stain with Melzer’s reagent. The subtending hypha has a color from yellowish to golden and presents a septum on spore base. Septoglomus mexicanum can be distinguished from all other Septoglomus species by spore size and color, by spore wall structure (four layers), and by color change of the subtending hypha. Phylogenetic analysis based on the AMF extended DNA barcode covering a 1.5-kb fragment of the small subunit (SSU), internal transcribed spacer region (ITS1-5.8S-ITS2), and the large subunit (LSU) of rRNA genes places S. mexicanum in the genus Septoglomus, separated from other described Septoglomus species, especially S. turnauae, with whom it could be confused morphologically. All available sequences in public databases suggest that this new fungal species has not yet been previously detected. Thus, there are currently 149 Glomeromycota species registered in Mexico, representing 47.4% of the known species worldwide.
... However, the role of mycorrhizal hyphae in the direct transfer of N has not been established well. Montesinos-Navarro et al. (2016) found a greater 15 N transfer to plants growing in vegetation patches with intact CMNs than in those treated with fungicide, which further provided evidence that CMNs can directly enhance nitrogen transfer among plants. Second, root exudates are absorbed straightaway by neighboring plants or they undergo mineralization prior to plant uptake, and then facilitate N transfer (Thilakarathna et al. 2016). ...
Aims
Mycorrhizae and root exudates have been considered the two important pathways for nitrogen (N) transfer from legume to non-legume plants. The present study aimed to investigate contribution of the relative importance of arbuscular mycorrhizal fungi and root exudates in short-term N transfer.
Methods
A field experiment was conducted to explore N transfer from alfalfa to maize under two different N application levels using ¹⁵N leaf labeling.
Results
N transfer amount ranged from 7 to 10 mg N plant⁻¹ from alfalfa to maize and significantly decreased (by 11%–22%) with N fertilizer application. Intercropping of 4 rows of maize and 6 rows of alfalfa with 30 cm intra-row spacing (IMA43) was the optimal intercropping mode, which increased N transfer, total N uptake and yield by 18%, 15% and 11%, respectively. The relative importance of arbuscular mycorrhizal fungi and root exudates on N transfer was dependent on soil N availability. Under no N addition, hyphal length density (HLD) of rhizosphere soil explained the largest significant amount (50%) of the variability in N transfer and crop yield. However, root exudates explained 77% of the variability in N transfer and crop yields with N fertilizer application.
Conclusions
Our findings highlighted that N transfer is reliant more on arbuscular mycorrhizal fungi than root exudates in N-deficient soil, whereas root exudates play a more important role in N-fertilized soil.
... However, some facilitative interactions can persist due to a minimization of competition (Valiente-Banuet and Verdú, 2008;Pausas and Verdú, 2010), or when the nurse plant also gains a benefit from the association (Pugnaire et al., 1996;Sortibrán et al., 2014;Tirado et al. 2015). Resource and nutrient transfer between plants might be an overlooked mechanism enhancing plant facilitative interactions (Montesinos-Navarro et al. 2016, 2017, 2018. Resource transfer from the nurse plants can enhance the performance and survival of facilitated seedlings, thereby potentially structuring plant communities (Simard et al., 1997, Dickie et al., 2002Teste et al., 2009;van der Heijden and Horton, 2009;Booth and Hoeksema, 2010). ...
... Soil fungal community forms mutualistic symbiotic associations with plant and soil to improve absorption of nutrients (Voøíšková and Baldrian, 2013). Until recently, studies of fungal ecology (community composition and diversity) have been greatly limited by the problems of morphological identification (Montesinos-Navarro et al., 2016;Tedersoo et al., 2016). High throughput sequencing have provided a new perspective to study soil fungal ecology in ecosystems (Mueller et al., 2014;Horn et al., 2017). ...
Previous studies have revealed inconsistent correlations between fungal diversity and plant/soil properties from local to global scales. Here, we investigated the internal relationships between soil fungal diversity and plant/soil properties on the Loess Plateau following vegetation restoration, using Illumina sequencing of the internal transcribed spacer 2 (ITS2) region for fungal identification. We found significant effects of land use types (Af, Artificial forest; Ns, Natural shrub; Ag, Artificial grassland; Ng, Natural grassland; Sc, slope cropland) on soil fungal communities composition, and the dominant phyla were Ascomycota, Basidiomycota, and Zygomycota, which transitioned from Basidiomycota-dominant to Ascomycota-dominant community due to vegetation restoration. The Chao1 richness, Shannon’s diversity and ACE indices were significantly influenced by land use types with the order of Ns > Af > Ng > Ag > Sc, and the total number of OTUs varied widely. In contrast, Good’s coverage and Simpson’s diversity indicated no significant difference among land use types (p > 0.05). Correlation analysis showed that plant and soil properties were closely related to fungal diversity regardless of land use types. In addition, soil organic carbon (SOC) and Hplant (plant richness, Shannon-Wiener index) were strong driving factors that explained fungal diversity. As revealed by the structural equation model (SEM) and generalized additive models (GAMs), fungal diversity was directly and indirectly affected by soil and plant properties, respectively, providing evidence for strong links between soil fungal diversity and plant and soil properties on the Loess Plateau.
Questions
A variety of mechanisms sustain diversity in natural communities as a result of ecological interactions between organisms. Competition has been studied extensively in the context of species maintenance, but facilitation is often conceptualized as simply reducing competition between functionally different species, which tends to decline throughout the plants' life span. Here we explore how interspecific facilitation may sustain diversity throughout the species' life by avoiding the extinction of locally rare species at juvenile stages and reducing performance disparities between neighbors of differing species at mature stages.
Methods
To do so, we measured whether rarer species relied more on facilitation than abundant ones in semiarid shrubland in southeast Spain. A mechanistic explanation of this relationship was subsequently tested by correlating rarity with the species' affinity to a particularly edaphic stressful environment. Finally, we assessed whether growing associated with neighbors in vegetation patches shaped by facilitation could balance performance disparities between species when they become adults.
Results
We show that facilitation (i) favors the rare species, which, in addition, tend to be those with low affinity to the stressful environment, and (ii) reduces the performance dissimilarities among plants growing associated within multispecific vegetation patches compared to plants growing alone.
Conclusions
These facilitative effects, beyond the reduction of competition between functionally similar species, might ensure positive and long‐lasting effects of biotic interactions, implying a more critical role for facilitation in preserving biodiversity than previously thought.
Mycorrhizae are mutualisms between plants and fungi that evolved over 400 million years ago. This symbiotic relationship commenced with land invasion, and as new groups evolved, new organisms developed with varying adaptations to changing conditions. Based on the author's 50 years of knowledge and research, this book characterizes mycorrhizae through the most rapid global environmental changes in human history. It applies that knowledge in many different scenarios, from restoring strip mines in Wyoming and shifting agriculture in the Yucatán, to integrating mutualisms into science policy in California and Washington, D.C. Toggling between ecological theory and natural history of a widespread and long-lived symbiotic relationship, this interdisciplinary volume scales from structure-function and biochemistry to ecosystem dynamics and global change. This remarkable study is of interest to a wide range of students, researchers, and land-use managers.
Le noyer anglais (Juglans regia L.) est la principale espèce cultivée pour la production de noix comestibles. Sa canopée peu dense et son système d'enracinement profond font du noyer une espèce idéale pour la culture en allées, une pratique agroforestière pouvant améliorer la productivité en favorisant les mécanismes de facilitation inter-plantes. L'agroforesterie du noyer fruitier nécessite la production à grande échelle de porte-greffes (PG) sélectionnés pour offrir le meilleur ancrage, la meilleure vigueur et la meilleure tolérance aux agents pathogènes. En raison de l'hétérozygotie du noyer qui ne reproduit pas à l'identique ces caractéristiques, la multiplication végétative in vitro joue un rôle clé dans la propagation des PG de noyer fruitier de qualité. La micropropagation des explants végétaux nécessite une phase d'acclimatation ex vitro pour réparer les anomalies induites in vitro, puis une post-acclimatation en serre lorsque les plantules deviennent photoautotrophes. Cependant, une faible survie et des taux de croissance lents sont des difficultés courantes rencontrées dans les pépinières lors de l'établissement de vitroplants. Comme beaucoup d'arbres fruitiers et à noix, le noyer présente une forte dépendance à l'égard des champignons mycorhiziens à arbuscules (MA) symbiotiques du sol pour sa nutrition phosphatée et son développement en raison de racines peu ramifiées qui limitent l'absorption du phosphate inorganique du sol (Pi). Dans le contexte de la production de PG de noyer fruitier, cette thèse a consisté à analyser, à différents stades de développement, l'établissement de sept PG présentant un intérêt économique, après inoculation ou non par un champignon MA dans des conditions contrastées de disponibilité en Pi. Nous avons démontré que la biotisation par le champignon MA Rhizophagus irregularis améliore le développement des PG lors de l'acclimatation ex vitro et post-vitro. Lors d'une carence en Pi, la biotisation augmente comparativement aux témoins les caractéristiques de performance des vitroplants, notamment la biomasse, le nombre de feuilles, la hauteur des tiges, l'efficacité photosynthétique et la nutrition foliaire (carbone, azote, Pi). Toutefois, ces avantages dépendent du PG, suggérant un recrutement différentiel de la voie d'absorption symbiotique du Pi selon le cultivar étudié. Ceci nous a conduit à identifier chez les Juglans spp. les transporteurs de Pi inductibles par la mycorhization. La détection des orthologues putatifs du transporteur de phosphate MtPT4 spécifique de la symbiose MA chez la légumineuse modèle Medicago truncatula, réalisée avec Orthofinder à l'aide de l'algorithme BLAST all-vs-all, a permis d'identifier trois orthologues putatifs chez J. regia et chez J. microcarpa. Nous avons validé ces candidats par l'étude comparative de leur expression après inoculation ou non par R. irregularis dans des conditions contrastées de disponibilité en Pi. Afin d'étudier les avantages de la mycorhization du noyer en culture en allées, nous avons simulé à l'aide de microcosmes compartimentés un système agroforestier dans lequel le PG RX1 (J. regia x J. microcarpa) est relié ou non par un réseau mycélien commun (RMC) à des racines de maïs (Zea maize L.), cultivé dans des conditions contrastées de disponibilité en Pi. En huit semaines, le réservoir de propagules fongiques formé par les racines de noyer a permis la mycorhization du maïs, autorisant ainsi un accès aux résidus de fertilisation. Nous avons montré que le RMC développé lors d'une carence en Pi conduit chez les deux plantes en co-culture à des bénéfices en termes de croissance et de nutrition, comparables à ceux observés sans mycorhization et sans carence. Cette étude démontre qu'un RMC peut pallier une carence phosphatée chez le maïs et le noyer élevés en co-culture, et donc contribuer à limiter l'apport d'intrants chimiques en systèmes agroforestiers.
Antecedentes y Objetivos:
“Bacanora” es una bebida espirituosa que emplea como materia prima principalmente las poblaciones silvestres de Agave angustifolia, las cuales requieren estrategias de conservación debido a su sobre aprovechamiento. El objetivo de este trabajo fue evaluar la variación morfológica y el contenido de azúcares reductores totales y fructanos del tallo de A. angustifolia proveniente de poblaciones silvestres conservadas en Sonora, México.
Métodos:
Se estudiaron tres poblaciones silvestres conservadas de A. angustifolia, en Sonora, México, en 29 variables relacionadas con las características morfológicas, indicadores de madurez fenológica y el contenido de azúcares reductores y fructanos.
Resultados clave:
El contenido de fructanos y azúcares reductores totales del tallo presentaron un promedio de 22.6 y 32.7 g/100 g (base seca) respectivamente; con una variación significativa entre las poblaciones silvestres (p<0.05). De las de 29 variables evaluadas, el estudio de componentes principales indicó que con cuatro componentes se explica 51.9% de la varianza de los datos. El análisis canónico discriminante de las 16 variables que mostraron mayor relación con los cuatro componentes principales definió el agrupamiento de las poblaciones. Dos funciones canónicas separaron significativamente (p<0.001) a las tres poblaciones silvestres de agave y representaron 100% de la varianza total.
Conclusiones:
Las variables con mayor contribución e importancia relativa asociadas a cada población fueron el desarrollo de la inflorescencia, el contenido de azúcares reductores totales del tallo, así como el tono y la saturación de color de las hojas.
Nitrogen (N) is an important macronutrient that has a significant role in plant growth and development. Therefore, optimum levels of N should be supplied to the plants for sustainable crop production. Besides the chemical fertilization of plants, beneficial soil microorganisms like the arbuscular mycorrhizal (AM) fungi form a mutualistic association with the majority of plant roots and enhance plant growth and nutrient uptake. The importance of AM fungi is mostly attributed to phosphorus (P) acquisition in plants. Nevertheless, the role of AM fungi in the N nutrition of plants is also well known. Plants N acquisition is mediated by direct and indirect pathways through plant roots or via a common mycelium network of AM fungi. Organic and inorganic N is the major source of N in the soils. Influence of AM fungi on other symbiotic and asymbiotic microorganisms is also known to contribute to dinitrogen (N2) fixation in plants. This chapter highlights the role of AM fungi in N nutrition, N2 fixation, and uptake of organic and inorganic N from the soils. Also, the importance of AM fungi in the N cycle and the impact of different AM fungal species on plant N uptake are discussed.
Seeds and seedlings are the most critical stages of cacti life cycles. From the thousands of seeds produced in a reproductive season, only a small fraction successfully germinate, the rest are lost to predation, go dormant and remain viable in the seed bank or lose viability. These early stages often depend on facilitation by nurse plants for germination and seedling recruitment. We aim to prescribe actions for the conservation of Cephalocereus polylophus by improving recruitment in the population. The viability of seeds with different storage times was evaluated as an indicator of their potential to form a short-term seed bank. Through the analysis of seed germination and seedling survival under the canopy of two nurse plant species and open areas, we assessed the importance of facilitation for recruitment. A predator exclusion experiment evaluated the intensity of herbivory on seeds and seedlings of different ages. Seeds had germination rates above 90\% under laboratory conditions, even after two years of storage. Seed germination was only registered under one of the two nurses and after two years, up to 4 % of the seedlings planted under both nurse plants survived and protection against herbivores increased seedlings survival. Considering that facilitation and age are crucial for seedling survival of C. polylophus , future conservation programs should include the protection of plant communities and the introduction of seedlings instead of seeds.
Mycorrhiza is a mutualistic symbiosis found in about 90% of the terrestrial plants. The arbuscular mycorrhiza (AM) and ectomycorrhiza (ECM), present in Eucalypt and Acacia, are the most studied in forests due to their importance in ecosystem productivity and sustainability in forestry. Here, our focus is to show recent results regarding their incidence, diversity, and functioning in planted forests, mainly those of Eucalyptus and Acacia spp. in consortia. Until recently, everybody assumed that arbuscular mycorrhizal fungi (AMF) were restricted to the uppermost 30 cm of soil. Yet, we evaluated their presence at the soil surface and in much deeper layers, since Eucalypt presents a root system that reaches down to about 20 m, still active in acquiring nutrients and water from deep reserves, which is of utmost importance during drought periods. In tropical soils of low pH and low fertility, with highly variable moisture levels, mycorrhiza provides better growth and higher tolerance to water deficiency and high temperatures, protection against pathogens, and greater efficiency in nutrient uptake. In short, mycorrhiza is a key factor of sustainability for Eucalypt stands in monoculture and in mixed plantations, mainly in tropical highly weathered soils.
Rice-fish mutualistic production systems rationalise the use of water and soil resources in an improved approach to sustainable food production. However, drivers of fungi community structure in paddy soil, including effects of nitrogen (N) application rate, are unclear in these systems. Here, we assessed soil fungi community and soil physicochemical responses in paddy soil to contrasting rates of N application in a rice-fish system. To clarify the mutualistic effects, the rice-fish system was compared with a standard rice monoculture under a 325.5 kg ha−1 N application rate. The results showed that N application rate affected abundance of paddy soil fungi (P < 0.05). Alpha diversity and richness of fungi were lower in the rice-fish system, but evenness increased with a decrease in N application rate, while the rate of N determined diversity of soil fungi in the rice-fish system. Dominant genera in the two systems differed, and soil physicochemical properties were more important drivers of soil fungi community structure in the rice-fish mutualistic system than in rice monoculture. Total N, available N and P regulated the abundance of dominant fungi. Our results indicate that management of soil fungi may contribute to sustainable agricultural production.
The tendency of closely related plant species to share natural enemies has been suggested to limit their co‐occurrence and performance, but we lack a deep understanding on how mutualistic interactions such as the mycorrhizal symbiosis affect plant–plant interactions depending on the phylogenetic relatedness of the interacting plants. We hypothesise that the effect of the mycorrhizal symbiosis on plant−plant facilitative interactions depends on the phylogenetic distance between the nurse and facilitated plants.
A recently published meta‐analysis compiled the strength of plant facilitative interactions in the presence or absence (or reduced abundance) of mycorrhizal fungi. We use phylogenetically informed Bayesian linear models to test whether the effect size is influenced by the phylogenetic distance between the plant species involved in each plant facilitative interaction.
Conspecific facilitative interactions are more strongly enhanced by mycorrhizal fungi than interactions between closely related species. In heterospecific interactions, the effect of the mycorrhizal symbiosis on plant facilitation increases with the phylogenetic distance between the nurse and facilitated plant species.
Our result showing that the effect of mycorrhizal symbiosis on the facilitation interactions between plants depends on their phylogenetic relatedness provides new mechanisms to understand how facilitation is assembling ecological communities.
Mycorrhizal symbiosis has important implications for the diversity and productivity of plant communities. However, our mechanistic understanding of its influence on the outcome of plant-plant interactions is still expanding. In this review we propose a framework that might be useful to efficiently approach the effects of mycorrhizal fungi (MF) on plant-plant interactions. We propose several scenarios that can theoretically result in different outcomes of plant-plant interactions based on the combination of two processes: the diversity of resources provided by MF taxa to their host (resource dissimilarity) and contrasting ways of distributing those resources (resource distribution). Then, we illustrate our arguments with different ecological contexts where certain combinations of these two processes are prone to occur. The proposed framework suggests testable hypotheses that can contribute to elucidate relevant processes underlying the effects of mycorrhizal symbiosis on plant-plant interactions.
Acaulospora alpina y Ambispora fennica se reportan por primera vez para México. Estos taxones se aislaron de la rizósfera de Adiantum capillus-veneris, Baccharis conferta, Quercus candicans, Q. crassifolia, Salvia lavanduloides y Selaginella lepidophylla que crecen en los bosques templados de México. Los especímenes revisados se describen en extenso y se comparan con las especies de hongos micorrizógenos arbusculares más parecidas.
Specificity in biotic interactions is mediated' by functional traits inducing shifts in the community species composition. Functional traits are often evolutionarily conserved, resulting in closely related species tending to interact with similar species. This tendency may initially shape the phylogenetic composition of coexisting guilds, but other intraguild ecological processes may either blur or promote the mirroring of the phylogenetic compositions between guilds. The roles of intra- and interguild interactions in shaping the phylogenetic community composition are largely unknown, beyond the mere selectivity in the interguild interactions. Plant facilitation is a phylogenetically structured species-specific process involving interactions not only between the same guild of plants, but also between plants and other guilds such as arbuscular mycorrhizal fungi (AMF). In this study it is hypothesized that reciprocal plant-AMF interactions will leave an interdependent phylogenetic signal in the community composition of both plants and AMF.
A correlation was used to test for a relationship between the phylogenetic composition of plant and AMF assemblages in a patchy xeric shrubland environment shaped by plant facilitation. In addition, a null model was used to test whether this correlation can be solely explained by selectivity in plant-AMF interactions.
A significant correlation was observed between the phylogenetic composition of plant and AMF assemblages. Plant phylogenetic composition in a patch was related to the predominance of plant species with high nursery quality that can influence the community assembly. AMF phylogenetic composition was related to the AMF phylogenetic diversity in each patch.
This study shows that shifts in the phylogenetic composition of plants and AMF assemblages do not occur independently. It is suggested that besides selectivity in plant-AMF interactions, inter-related succession dynamics of plants and AMF within patches could be an ecological mechanism driving community assembly. Future lines of research might explore whether interlinked above- and below-ground dynamics could be occurring across multiple guilds simultaneously.
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Obligate aerobic AMF taxa have high species richness under waterlogged conditions, but their ecological role remains unclear. Here we focused on AM fungal mediation of plant interactions in a marshland plant community. Five cooccurring plant species were chosen for a neighbor removal experiment in which benomyl was used to suppress AMF colonization. A Phragmites australis removal experiment was also performed to study its role in promoting AMF colonization by increasing rhizosphere oxygen concentration. Mycorrhizal fungal effects on plant interactions were different for dominant and subdominant plant species. AMF colonization has driven positive neighbor effects for three subdominant plant species including Kummerowia striata, Leonurus artemisia, and Ixeris polycephala. In contrast, AMF colonization enhanced the negative effects of neighbors on the dominant Conyza canadensis and had no significant impact on the neighbor interaction to the dominant Polygonum pubescens. AM colonization was positively related to oxygen concentration. P. australis increased oxygen concentration, enhanced AMF colonization, and was thus indirectly capable of influencing plant interactions. Aerobic AM fungi appear to be ecologically relevant in this wetland ecosystem. They drive positive neighbor interactions for subdominant plant species, effectively increasing plant diversity. We suggest, therefore, that AM fungi may be ecologically important even under waterlogged conditions.
Methodologies based on 15N-enrichment for estimating the transfer of nitrogen (N) between legumes and companion non-legume species in agro-ecosystems are critically reviewed and classified according to whether they (i) are direct or indirect (ii) are dependent or independent of the measurement of yield and (iii) are estimating transfer of legume N, biologically-fixed legume N, or non-legume N. The two most commonly used methods are the indirect 15N isotope dilution method and the direct 15N shoot-labelling method. Published estimates both within and between agro-ecosystems are very variable, ranging from 0 to >50% of the N present in a companion species estimated to have been derived from a companion legume. The transfer of N also occurs from companion species to legumes, but is generally much less than the opposite flux. Factors conducive to N transfer include inter alia species proximity (i.e. intimacy of root contact), legume pruning, defoliation or death and the length of the transfer period. It was concluded that two methodologies (15N2 exposure and the split-root technique) lack field applicability. New insights into the various mechanisms of N transfer in agro-ecosystems may assist in the selection or development of more appropriate methodologies for estimating N transfer by both above- and below-ground pathways.
Ectomycorrhizal (EM) networks are hypothesized to facilitate regeneration under abiotic stress. We tested the role of networks in interactions between P. menziesii var. glauca trees and conspecific seedlings along a climatic moisture gradient to: (1) determine the effects of climatic factors on network facilitation of Pseudotsuga menziesii (Mirb.) Franco var. glauca (Mayr) seedling establishment, (2) infer the changing importance of P. menziesii var. glauca parent trees in conspecific regeneration with climate, and (3) parse the competitive from facilitative effects of P. menziesii var. glauca trees on seedlings. When drought conditions were greatest, seedling growth increased when seedlings could form a network with trees in the absence of root competition, but was reduced when unable to form a network. Survival was maximized when seedlings were able to form a network in the absence of root competition. Seedling stem natural abundance δ13C increased with drought due to increasing water use efficiency, but was unaffected by distance from tree or network potential. We conclude that P. menziesii seedlings may benefit from the presence of established P. menziesii trees when growing under climatic drought, but that this benefit is contingent upon the establishment of an EM network prior to the onset of summer drought. These results suggest that networks are an important mechanism for EM plants establishing in a pattern consistent with the stress-gradient hypothesis, and therefore the importance of EM networks to facilitation in regeneration of EM trees is expected to increase with drought.
Mycorrhizal networks, defined as a common mycorrhizal mycelium linking the roots of at least two plants, occur in all major terrestrial ecosystems. This review discusses the recent progress and challenges in our understanding of the characteristics, functions, ecology and models of mycorrhizal networks, with the goal of encouraging future research to improve our understanding of their ecology, adaptability and evolution. We focus on four themes in the recent literature: (1) the physical, physiological and molecular evidence for the existence of mycorrhizal networks, as well as the genetic characteristics and topology of networks in natural ecosystems; (2) the types, amounts and mechanisms of interplant material transfer (including carbon, nutrients, water, defence signals and allelochemicals) in autotrophic, mycoheterotrophic or partial mycoheterotrophic plants, with particular focus on carbon transfer; (3) the influence of mycorrhizal networks on plant establishment, survival and growth, and the implications for community diversity or stability in response to environmental stress; and (4) insights into emerging methods for modelling the spatial configuration and temporal dynamics of mycorrhizal networks, including the inclusion of mycorrhizal networks in conceptual models of complex adaptive systems. We suggest that mycorrhizal networks are fundamental agents of complex adaptive systems (ecosystems) because they provide avenues for feedbacks and cross-scale interactions that lead to self-organization and emergent properties in ecosystems. We have found that research in the genetics of mycorrhizal networks has accelerated rapidly in the past 5 y with increasing resolution and throughput of molecular tools, but there still remains a large gap between understanding genes and understanding the physiology, ecology and evolution of mycorrhizal networks in our changing environment. There is now enormous and exciting potential for mycorrhizal researchers to address these higher level questions and thus inform ecosystem and evolutionary research more broadly.
Companion or nursing taxa may aid the establishment of agricultural and forestry crops by improving soil N status (if legume) and soil structure, and by reducing soil erosion and suppressing weedy species. This study's objectives were to test the applicability of soybean and weeping love grass as companion plants for assisting Pinus patula establishment on former agricultural lands (oldlands), and their capacity for suppressing growth of weedy species. Two experimental trials were conducted which involved growing pine, soybean, weeping love grass and an assortment of weedy species in monocultures and mixtures in pots containing oldland and plantation soils. Pine height and stem diameter were measured at monthly intervals, with total biomass accumulation in all taxa determined 14 months after planting. In the presence of soybean, both shoot and root growth of pine seedlings were enhanced, but root growth was reduced in the presence of weeping love grass. In the presence of the weedy species assortment, pine stem diameter, height, shoot and root biomass were all decreased. In contrast, total biomass accumulation of both soybean and weeping love grass was unaffected by the presence of the weed species assortment. However, the total biomass of this assortment was reduced in the presence of these two species. It is concluded, that P. patula establishment on oldlands infested with agronomic weeds may be improved by cultivating this species together with soybean.
1.Labelling plants with 15N and 13C stable isotopes usually require cultivation of plants in isotopically enriched soil and gas-tight labelling chambers - both approaches are not suitable if one aims to investigate in situ species interactions in real plant communities.
2.In this greenhouse experiment, we tested a labelling method in which dual-labelled (15N, 13C) urea solution is brushed directly onto leaves of twelve temperate grassland species representing grasses, non-leguminous forbs and legumes.
3.Across all plant species, shoots (15N: 0·145; 13C: 0·090 atom percent excess, APE) and roots (15N: 0·051; 13C: 0·023 APE) were significantly enriched after five daily labelling events. Generally, isotopic enrichments were significantly higher in shoots than in roots. No clear pattern of absolute isotopic enrichment was observed between plant functional groups; however, grasses showed a more even allocation between shoots and roots than forbs and legumes. Isotopic enrichment levels after 4 weeks were lower, higher or unchanged compared to those of week one and varied between species or plant parts.
4.Considering the consistent enrichment levels and simplicity of this method, we conclude that it can be applied widely in ecological studies of above-belowground plant–plant or plant–animal interactions even in real plant communities.
Question
Regeneration failure and gradual tree dieback are major threats for the persistence of savanna‐like grazed oak woodlands. Current research has argued that the scarcity of ‘safe sites’, in particular shrubs, is the main cause of the lack of effective tree recruitment. But can different shrub species be considered as safe sites generally? Do two distinct shrub species, with contrasted life strategies, affect several life stages of tree regeneration in similar ways or do they specifically influence the recruitment process?
Location
Holm oak woodlands of SW I berian P eninsula (40°02′ N, 06°06′ W).
Methods
We surveyed densities of recently emerged and surviving seedlings as well as small and large saplings over two consecutive years in 40 sites that were independently managed, comparing plots encroached by either C istus ladanifer (a shallow‐rooted shrub, forming dense populations, with reported allelopathic compounds) or R etama sphaerocarpa (a N 2 ‐fixing, deep‐rooted shrub that forms scattered populations) vs their respective control plots (without shrubs). To assess the effect of mature trees and both shrub species on the performance and survival of recently emerged oak seedlings, we established an acorn sowing experiment in the same surveyed microhabitats (open spaces, shrub, tree and tree–shrub).
Results
The survey showed that both shrubs species had a positive effect at early recruitment stages. At later life stages, this effect weakened under C istus whereas it strengthened under Retama . The acorn sowing experiment showed that both shrub species buffered abiotic conditions and enhanced seedling functioning similarly, but R etama enhanced seedling survival to a higher extent than C istus .
Conclusions
The two shrub species impose a specific template that is able to affect the long‐term dynamics of M editerranean oak woodlands. C istus shrubs are effective in protecting seedlings physically against herbivores and facilitate early survival, but may compete with older stages of oak regeneration. In contrast, R etama shrubs exert stronger biological facilitation and guarantee long‐term persistence of surviving seedlings. We argue that improved understanding of the effectiveness of different nurse plants and their contrasting factors is of major interest for the conservation and restoration of degraded oak woodlands.
Different plant species can be compatible with the same species of mycorrhizal fungi, and be connected to one another by a common mycelium,. Transfer of carbon, nitrogen, and phosphorus, through interconnecting mycelia has been measured frequently in laboratory experiments, but it is not known whether transfer is bidirectional, whether there is a net gain by one plant over its connected partner, or whether transfer affects plant performance in the field,. Laboratory studies using isotope tracers show that the magnitude of one-way transfer can be influenced by shading of `receiver' plants,, fertilization of `donor' plants with phosphorus, or use of nitrogen-fixing donor plants and non-nitrogen-fixing receiver plants,, indicating that movement may be governed by source-sink relationships. Here we use reciprocal isotope labelling in the field to demonstrate bidirectional carbon transfer between the ectomycorrhizal tree species Betula papyrifera and Pseudotsuga menziesii, resulting in net carbon gain by P. menziesii. Thuja plicata seedlings lacking ectomycorrhizae absorb small amounts of isotope, suggesting that carbon transfer between B. papyrifera and P. menziesii is primarily through the direct hyphal pathway. Net gain by P. menziesii seedlings represents on average 6% of carbon isotope uptake through photosynthesis. The magnitude of net transfer is influenced by shading of P. menziesii, indicating that source-sink relationships regulate such carbon transfer under field conditions.
1. Almost all plants are engaged in symbiotic relationships with mycorrhizal fungi. These soil fungi can promote plant growth by supplying limiting nutrients to plant roots in return for plant assimilates.
2. Many mycorrhizal fungi are not host specific and one fungal individual can colonize and interconnect a considerable number of plants. The existence of these so-called mycorrhizal networks implies that fungi have the potential to facilitate growth of other plants and distribute resources among plants irrespective of their size, status or identity. In this paper, we explore the significance of mycorrhizal fungal networks for individual plants and for plant communities.
3. We address the following questions: (i) are all plant species benefitting from mycorrhizal networks, (ii) is benefit dependent on the size or age of a plant, (iii) is fungal support related to the relative dominance of plants in a community, (iv) are there host dependent barriers and physiological constraints for support and (v) what is the impact of mycorrhizal networks on plant–plant interactions and plant community dynamics? Moreover, using a review of published studies, we test whether mycorrhizal networks facilitate growth of small seedlings that establish between or near larger plants.
4. We found 60 cases where seedling species were grown together with larger plants with or without mycorrhizal fungal networks. Mycorrhizal networks promoted seedling growth in 48% of the cases (for 21 seedling species), while negative effects (25%) and no effects (27%) were also common. Seedlings associating with ectomycorrhizal fungi benefitted in the majority of the cases while effects on seedlings associating with arbuscular mycorrhizal fungi were more variable. Thus, the facilitative effects of mycorrhizal fungal networks depend on seedling species identity, mycorrhizal identity, plant species combinations and study system. We present a number of hypothetical scenarios that can explain the results based on cost–benefit relationship of individual members in a network.
5.Synthesis. Overall, this review shows that mycorrhizal networks play a key role in plant communities by facilitating and influencing seedling establishment, by altering plant–plant interactions and by supplying and recycling nutrients.
Positive interactions and interdependence in plant communities offers a new look at an old problem – the nature of the communities. This book marshals ecological literature from the last century on facilitation to make the case against the widely accepted "individualistic" notion of community organization. Clearly, many species in many communities would not be present without the ameliorating effects of other species. In other words, communities are not produced only by summing the population ecology of species. Concepts covered include the idea that positive interactions are more prevalent in physically stressful conditions, species specificity in facilitative interactions, indirect facilitative interactions, how facilitation contributes to diversity-ecosystem function relationships, and potential evolutionary aspects of positive interactions.
The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular‐arbuscular mycorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean [Glycine max (L.) Merr.], were grown in association with a dwarf maize (Zea mays L.) cultivar in containers which interposed a 6‐cm‐wide root‐free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 μm) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N‐sufficient soybean plants through N2‐fixation or N‐fertilization on associated maize‐plant growth and nutrition were compared to those of an N‐deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N‐fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N‐deficient association. When maize was grown with nodulated soybean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N‐fertilized treatment. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N‐fertilized soybean plants was more advantageous to maize than was association with the N2‐fixing ones.
In developed forests and secondary successional sites, host plants can readily access ectomycorrhizal (ECM) fungi because of the ubiquitous ECM mycelia and spores in soil, but this is not the case in some primary successional sites. In a volcanic desert on Mt Fuji, Japan, most of the area is non-mycorrhizal habitat and has poorly developed soil spore-banks. ECM habitat, i.e. pioneer willow shrubs and a small surrounding area containing ECM mycelia, are quite sparsely distributed, accounting for about 1 % of the ground surface in total. Such unique conditions provide us an interesting opportunity to explore the magnitude and role of direct mycelial connections between plants, i.e. ECM networks, in the field. It is difficult to observe individual ECM mycelial spread in soil, but the distribution of sporocarps and ECM roots having the same genotype indicate the spread of a mycelium in soil. We applied microsatellite markers to genotype sporocarps and ECM tips, and found that genets of two pioneer Laccaria species were small in size (mostly <1 m) and ephemeral. In contrast, genets of Scleroderma included some long-lived large genets (>10 m). These results indicate that ECM networks could vary considerably in size and longevity, even in the same site and associated with the same host species. Field transplanting experiment revealed that current-year willow seedlings rarely formed ECM associations in most habitats of the desert and showed poor growth. ECM infection from spores did not significantly improve seedling growth, indicating a small isolated mycelium on a tiny seeding may not be enough to acquire sufficient nutrients from extremely nutrient poor scoria. In contrast, seedlings transplanted near the pre-established willow shrubs, where ECM networks are available, readily formed ECM associations and grew well. Moreover, artificially reproduced ECM networks in previously non-mycorrhizal habitats significantly improved the growth of connected seedlings in 10 of 11 ECM fungal species in this desert. Therefore, ECM networks appear to be mostly positive and could be critical to seedling establishment, at least in this primary successional setting. Some previously proposed mechanisms may be less relevant to the observed positive effect of ECM networks on seedling establishment. For example, plant-to-plant carbon transfer through ECM networks might work for seedlings in dark forest floor, but not in primary successional settings characterized by strong sun light. More relevant mechanisms should include rapid ECM colonization with low costs, larger absorbing surface area than a solitary mycelium, and nutrient translocation within a network from nutrient rich soil patches to most demanding parts, often seedlings.
Arbuscular mycorrhizal (AM) fungi are one of the most important groups of plant symbionts. These fungi provide mineral nutrients to plants in exchange for carbon. Although substantial amounts of resources are exchanged, the factors that regulate trade in the AM symbiosis are poorly understood. Recent evidence for the reciprocally regulated exchange of resources by AM fungi and plants has led to the suggestion that these symbioses operate according to biological market dynamics, in which interactions are viewed from an economic perspective, and the most beneficial partners are favoured. Here we present five arguments that challenge the importance of reciprocally regulated exchange, and thereby market dynamics, for resource exchange in the AM symbiosis, and suggest that such reciprocity is only found in a subset of symbionts, under specific conditions. We instead propose that resource exchange in the AM symbiosis is determined by competition for surplus resources, functional diversity and sink strength.
The role of arbuscular mycorrhizas in the transfer of N and P between pea (Pisum sativum L.) and barley (Hordeum vulgare L.) plants was studied in a controlled environment. The plants were grown together in PVC containers, either in symbiosis with Glomus intraradices Schenck and Smith or as non-mycorrhizal controls, and with their root systems separated by an intermediate buffer zone (2 cm), confined by fine nylon mesh. The pea donor plants were supplied simultaneously with 15N and 32P, using a split-root labelling technique, in order to follow the flow of N and P to the barley receiver plants during 60 d of growth. In half of the containers, the donor-plant shoot was removed 42 d after the start of labelling and the roots were left in the soil to decompose. The reverse transfer of N and P, from barley donor to pea receiver plants was also measured to allow calculation of the net transfer through hyphae between mycorrhizal donor and receiver plants. No significant transfer of N was detected from intact pea donor plants to the barley receiver plants in the non-mycorrhizal controls. Mycorrhizal colonization slightly increased the transfer of N. However, the net transfer of N was almost insignificant since N was also transferred in the reverse direction, from barley to pea. Removal of the pea donor-plant shoots increased the N transfer to 4% of the donor-root N in the non-mycorrhizal controls. Contrastingly, 15% of the donor-root N was transferred to the receiver plants, when plants were colonized by G. intraradices. The results for P transfer followed the same patterns as was observed for N, although in smaller proportions. The results indicate that arbuscular mycorrhizas may play a significant role in the flow of N and P between two plants interconnected by hyphae, when the root system of one of the plants is decomposing.
Positive interactions and interdependence in plant communities offers a new look at an old problem - the nature of the communities. This book marshals ecological literature from the last century on facilitation to make the case against the widely accepted "individualistic" notion of community organization. Clearly, many species in many communities would not be present without the ameliorating effects of other species. In other words, communities are not produced only by summing the population ecology of species. Concepts covered include the idea that positive interactions are more prevalent in physically stressful conditions, species specificity in facilitative interactions, indirect facilitative interactions, how facilitation contributes to diversity-ecosystem function relationships, and potential evolutionary aspects of positive interactions.
Facilitation has been proposed to be a fundamental mechanism for plant coexistence, being particularly important in highly stressful environments such as alpine environments. In this type of environment, species called “cushion plants” can ameliorate the stressful conditions, acting as nurses for other plants. Of the several mechanisms proposed in the positive-interactions framework, plant–microorganism interaction may be one of the most common, but least documented. Here we show that the presence of endophytes isolated from the roots of cushion plants Laretia acaulis can play a fundamental role in the establishment, performance and survival of both native and exotic plant seedlings that are known to be facilitated by the cushion species.
This paper reports the effect of twenty-five commonly used fungicides in agriculture on two arbuscular mycorrhizal fungi (AMF) present in commercial products of ATENS, S.L.: Glomus intraradices (Schenck & Smith) and Glomus mosseae [(Nicol. & Gerd.) Gerdemann & Trappe], forming the symbiosis with leek plants. Systemic fungicides (Aliette, Beltanol, Caddy 10, Forum, Moncut, Ortiva, Previcur, Ridomil Gold MZ, Ridomil Gold SL, Rubigan, Sinthane, Stroby, Swich, Tachigarem, Teldor, Topas 10 EC, Frupica) and non systemic fungicides (Daconil 75%, Ditiver, Euparem, INACOP, Octagón, Parmex, Terrazole and Metaram), started to be applied to soil and leaves at recommended concentrations and frequencies 4 weeks after transplant and AMF inoculation. The effect of the fungicides was assessed by comparing treated and untreated plants that were inoculated with the AMF through quantification of root mycorrhizal colonization. Among the fungicides applied to the soil, Octagon, Ditiver, Parmex and Metaram virtually eliminated the mycorrhizal symbiosis in treated plants, while the mycorrhizal colonization was not affected by the soil treatment with Beltanol, INACOP and Previcur. Three fungicides of foliar recommended application: Rubigan, Frupica, and Sinthane, strongly inhibited mycorrhizal colonization, but Aliette, Forum, Teldor, Swich and Ortiva, did not seem to reduce it substantially. In addition, the work describes the individual effect of each fungicide applied on both, foliage and soil.
The role of arbuscular mycorrhizas in the transfer of N and P between pea (Pisum sativum L.) and barley (Hordeum vulgare L.) plants was studied in a controlled environment. The plants were grown together in PVC containers, either in symbiosis with Glomus intraradices Schenck and Smith or as non-mycorrhizal controls, and with their root systems separated by an intermediate buffer zone (2 cm), confined by fine nylon mesh. The pea donor plants were supplied simultaneously with 15N and 32P, using a split-root labelling technique, in order to follow the flow of N and P to the barley receiver plants during 60 d of growth. In half of the containers, the donor-plant shoot was removed 42 d after the start of labelling and the roots were left in the soil to decompose. The reverse transfer of N and P, from barley donor to pea receiver plants was also measured to allow calculation of the net transfer through hyphae between mycorrhizal donor and receiver plants. No significant transfer of N was detected from intact pea donor plants to the barley receiver plants in the non-mycorrhizal controls. Mycorrhizal colonization slightly increased the transfer of N. However, the net transfer of N was almost insignificant since N was also transferred in the reverse direction, from barley to pea. Removal of the pea donor-plant shoots increased the N transfer to 4% of the donor-root N in the non-mycorrhizal controls. Contrastingly, 15% of the donor-root N was transferred to the receiver plants, when plants were colonized by G. intraradices. The results for P transfer followed the same patterns as was observed for N, although in smaller proportions. The results indicate that arbuscular mycorrhizas may play a significant role in the flow of N and P between two plants interconnected by hyphae, when the root system of one of the plants is decomposing.
Facilitative interactions are defined as positive effects of one species on another, but bidirectional feedbacks may be positive, neutral, or negative. Understanding the bidirectional nature of these interactions is a fundamental prerequisite for the assessment of the potential evolutionary consequences of facilitation.
In a global study combining observational and experimental approaches, we quantified the impact of the cover and richness of species associated with alpine cushion plants on reproductive traits of the benefactor cushions.
We found a decline in cushion seed production with increasing cover of cushion-associated species, indicating that being a benefactor came at an overall cost. The effect of cushion-associated species was negative for flower density and seed set of cushions, but not for fruit set and seed quality. Richness of cushion-associated species had positive effects on seed density and modulated the effects of their abundance on flower density and fruit set, indicating that the costs and benefits of harboring associated species depend on the composition of the plant assemblage.
Our study demonstrates 'parasitic' interactions among plants over a wide range of species and environments in alpine systems, and we consider their implications for the possible selective effects of interactions between benefactor and beneficiary species.
The N flow dynamics in grass–clover mixtures are not well understood. Spatial distributions and temporal differences in inter- and intra-species N transfer were investigated at field sites in Iceland, Germany, and Denmark, with three different managements at the Danish site. Both grass and white clover were leaf-labeled four times during a full year and the short-term N transfer to neighboring grass and white clover was determined in 10 cm intervals up to 1 m from the labeled plant. In addition 15N-injection of inorganic N at 5, 15, and 25 cm soil depth was carried out at the Danish site to compare spatial and temporal N transfer patterns to soil inorganic N uptake. The short-term N transfer from white clover to the closest companion grass reached levels of more than 50% of N from labeled white clover late in the growing season, thus questioning whether longer-term root turnover processes are dominating N transfer. The horizontal N transfer to grass exceeded 50 cm from the labeled plant at one site. The study showed that the competitive ability of white clover is as important for N dynamics in grass–white clover mixtures as that of the companion grass. Intra-species N transfer showed that both grass and white clover have reuptake of deposited N corresponding to at least 1% of the N found in leaf biomass. The study also showed that N transfer cannot be explained simply by competition for soil inorganic N, which indicates transfer via organic N forms.
Seasonal variation in N2 fixation, N transfer from clover to ryegrass, and soil N absorption in white clover–ryegrass swards were investigated under field conditions over three consecutive years. The plots were established with different seeding ratios of clover and ryegrass and contrasting fertilizer N ranging from 3 to 72 kg ha-1 year-1.
An initially poor clover population needed at least one growing season to reach the same yield output as an initially well established clover population. The clover content of the sward decreased by the annual application of 72 kg N ha-1 but not by smaller N dressings.
The total amount of atmospherically derived N in clover growing in mixture with ryegrass was, on average over the three years equal to 83, 71, 68 and 60 kg N ha-1 for the treatments of 3, 24, 48 and 72 kg N ha-1, respectively. The proportion of atmospherically derived N declined with increasing N application, but never became smaller than 80% of total clover N. The proportion of atmospherically derived N in a pure stand white clover amounted to 60–80% of the total N content, equivalent to 109, 110, 103 and 90 kg N ha-1 for the treatments of 3, 24, 48 and 72 kg N ha-1, respectively.
Only small amounts of atmospherically derived N was transferred to the associated ryegrass during the first production year, while in each of the following years up to 21 kg ha-1 was transferred. The average amount of N transferred from clover to ryegrass was equivalent to 3, 16 and 31% of the N accumulated in ryegrass in the first, second and third production year, respectively. Expressed relative to the total amount of fixed N2 in the clover–ryegrass mixture, the transfer amounted to 3, 17 and 22% in the first, second and third production year, respectively. Thus transfer of atmospherically derived N from clover contributed significantly to the N economy of the associated ryegrass.
The clover–ryegrass mixture absorbed constantly higher amount of soil derived N than the pure stands of the two species. Only 11% of the total accumulated fertilizer N and soil derived N in the mixture was contained within the clover component. Lower water use efficiencies for the plants grown in mixture compared to pure stands were mainly related to the increased N uptake in the mixture, with the subsequent increase in growth compared to the pure stands.
It is concluded that positive interactions between clover and ryegrass growing in mixture ensure a more efficient fixation of atmospheric N2 and absorption of fertilizer N and soil derived N than pure stands of the same species.
Ectomycorrhizal (ECM) fungi are symbiotic microorganisms that can significantly improve the water and nutrient uptake of host plants. With reference to ECM fungi, we studied the effects of established shrubs on the subsequent seedling establishment of three woody plant species in a volcanic desert on Mt. Fuji, Japan, during early primary succession. Salix reinii, an alpine dwarf willow, is the pioneer ECM plant at this research site, and many ECM fungi have colonized established willow shrubs. ECM formation was found to be high on S. reinii seedlings that had been transplanted near established willow shrubs. The growth and nitrogen content of the seedlings increased significantly with the numbers of associated ECM fungal species and ECM root tips. ECM formation on transplanted seedlings of Betula ermanii and Larix kaempferi, two subsequent successional tree species, was also higher near the established willow shrubs. Molecular identification showed that almost all of the ECM fungi on transplanted seedlings of the three plant species were of the same species as those observed on the established willow shrubs. These results indicate that ECM fungi associated with established willow shrubs are essential in facilitating seedling establishment of successional plant species in the early successional volcanic desert.
It is well known from laboratory studies that a single mycorrhizal fungal isolate can colonize different plant species, form interplant linkages, and provide a conduit for interplant transfer of isotopic carbon, nitrogen, phosphorus, or water. There is increasing laboratory and field evidence that the magnitude and direction of transfer is influenced by physiological source-sink gradients between plants. There is also evidence that mycorrhizal fungi play a role in regulating transfer through their own source-sink patterns, frequency of links, and mycorrhizal dependency. Although it is plausible that connections are extensive in nature, field studies have been hampered by our inability to observe them in situ and by belowground complexity. In future, isotopic tracers, morphological observations, microsatellite techniques, and fluorescent dyes will be useful in the study of networks in nature. Mycorrhizal networks have the potential to influence patterns of seedling establishment, interplant competition, plant diversity, and plant community dynamics, but studies in this area are just beginning. Future plant community studies would benefit from concurrent experimental use of fungal network controls, isotopic labeling, direct observation of interplant linkages, and long-term observation in the field. In this paper, we review recent literature on mycorrhizal networks and interplant carbon transfer, suggest future research directions, and highlight promising scientific approaches.
1. The relative contribution of positive and negative interactions to the organization of ecological communities is an important area, though poorly understood because of the complexity inherent to long-term interactions. For example, positive interactions like plant facilitation turn into negative interactions (competition) along the ontogeny of a plant or in response to temporal fluctuations in the environment. Furthermore, when many plants grow together indirect effects are usually positive and alleviate direct competitive effects.
2. The large number of direct and indirect interactions potentially occurring in natural communities and the temporal scale necessary to account for the ontogenetic shifts in the sign of the interaction makes a fully experimental approach prohibitive. Here, we propose that the phylogenetic distance among co-occurring species is a good proxy to detect competition as a long-term force assembling community composition. Our proposal is based on the observation that closely related species tend to be phenotypically similar and therefore compete for the same niche.
3. We test the relationship between phylogenetic relatedness and the persistence of pairwise (nurse-facilitated) interactions occurring between 102 woody species in three Mexican semi-arid communities in order to quantify the balance between competition and facilitation at the community level.
4. Our results indicate that facilitation turns into competition with increasing taxa relatedness. After validating the association between competition and phylogenetic relatedness, we estimate that 57% of the interactions remain with time while 43% become competitive. [Correction added after publication, 4 March 2008: in the preceding sentence, values corrected from 53% and 47%, respectively.] The preponderance of positive interactions may be explained if facilitation is considered as a mutualism in which both species benefit leading to vegetation clumps in communities.
5. Synthesis . We provide a new perspective on the balance between positive and negative interactions based on a phylogenetically structured network of interactions. This approach promises to contribute to our understanding of long standing issues in plant ecology and to reveal new areas of future research by testing the existence and the nature of the mutualisms as well as their complexity–stability properties on communities as a whole.
Below-ground transfer of nitrogen (N) fixed by legume trees to associated non-N2-fixing crops has received little attention in agroforestry, although the importance of below-ground interactions is shown in other ecosystems. We used 15N natural abundance to estimate N transfer from the legume tree Gliricidia sepium (Jacq.) Kunth ex Walp. to C4 grass Dichanthium aristatum (Poir.) C.E. Hubb. in a silvopastoral system, where N was recycled exclusively by below-ground processes and N2 fixation by G. sepium was the sole N input to the system. Finding a suitable reference plant, a grass without contact with tree roots or litter, was problematic because tree roots invaded adjacent grass monocrop plots and soil isotopic signature in soil below distant grass monocrops differed significantly from the agroforestry plots. Thus, we used grass cultivated under greenhouse conditions in pots filled with agroforestry soil as the reference. A model of soil 15N fractionation during N mineralization was developed for testing the reliability of that estimate. Experimental and theoretical results indicated that 9 months after greenhouse transplanting, the percentage of fixed N in the grass decreased from 35% to
Pruning of hedgerow trees is an important management practice for the successful establishment of an alley cropping system. Although pruning affects biomass production, only meager evidence of this management on distribution of nutrients among the different plant organs after tree regrowth is available. This study examined the effect of pruning on the distribution and use efficiency of N and P in a N2 fixing leguminous tree species, Gliricidia sepium, and two non-N2 fixing leguminous tree species, Senna siamea and S. spectabilis, grown in a field on an Alfisol (low in P) at Fashola (Guinea Savanna Zone), Southwestern Nigeria. Four P rates, 0, 20, 40 and 80 kg P ha-1 as single superphosphate were used and management treatments included pruned versus unpruned plants. The 15N isotope dilution technique was used to measure N2 fixation in G. sepium. Partitioning of total P among different plant organs was influenced by plant species and pruning management, but was not affected by P application rates. The distribution of total P in the various plant organs followed that of dry matter yield while N partitioning had a different pattern. Pruned plants distributed about 118% more total P to branches and had a higher physiological P use efficiency (PPUE) than unpruned plants. Leaves were the biggest sink for total N and N allocation in the other plant organs was influenced by plant species and pruning management, G. sepium had relatively more of its total N and P partitioned into roots (about double that of the non-N2 fixing trees) but had a lower PPUE. Unpruned and pruned G. sepium derived 35 and 54% respectively of their total N from atmospheric N2, with about 54% of the fixed N2 being allocated to leaves and roots. Results showed that N and P pools turned over in the branches during plant regrowth after pruning but the causative factors associated with this phenomenon were not clear.
Publisher Summary The chapter discusses mycorrhiza, a symbiotic, non-pathogenic association between a plant root and a fungus. This paper first summarizes evidence that mycorrhizal links between plants that occur. It then reviews evidence on various possible functions of these links, and finally considers if there is any evidence that the links influence the species composition and structure of plant communities, and ecosystem processes such as nutrient cycling. Evidence on almost every aspect of mycorrhizal links and their possible roles is inadequate; any conclusions must therefore be preliminary and tentative. There is evidence that seedlings can become infected by forming mycorrhizal links with established plants, and growth of seedlings of some species is faster under these conditions. Transfer of I4C from one plant to another via mycorrhizal links can occur, but it is not clear that net transfer of organic compounds is ever great enough to increase significantly growth or survival of the receiver plant. There is no clear evidence that mycorrhizal links prevent these relationships from occurring or introduce fundamentally new interactions between plants. The evidence so far available suggests that mycorrhizal links can alter the relationships between plants, but that they do so by modifying competition and nutrient cycling rather than replacing them.
summaryThe fungicide ‘Rovral’ (iprodione) was applied in granular form in an attempt to reduce VA mycorrhizal infection of plants during the early stages of secondary plant succession, namely the first year of colonization of bare ground. In 7 out of 11 plant species examined, infection levels were reduced by the fungicide. Four of these also showed reduced cover abundance as a result of fungicide application. Since three were annual forbs, which as a plant life-history grouping comprised 73 % of the community, total cover of the vegetation (as measured by point quadrats) was significantly reduced by the fungicide. In three species, reduced infection levels did not appear to result in reduced vegetation cover. The reasons for this are discussed in relation to the dependency of plants on mycorrhizal infection. It was found that fewer plant species recruited into communities where iprodione was applied. The implications of these results, in terms of the role that mycorrhizas play in the structuring of early successional plant communities, are discussed.
To eliminate possible confusion in the reporting of isotopic abundances on noncorresponding scales, the Commission on Atomic Weights and Isotopic Abundances recommended at the 37th General Assembly at Lisbon, Portugal that (i) 2H/1H relative ratios of all substances be expressed relative to VSMOW (Vienna Standard Mean Ocean Water) on a scale such that 2H/1H of SLAP (Standard Light Antarctic Precipitation) is 0.572 times that of VSMOW, (ii) 13C/12C relative ratios of all substances be expressed relative to VPDB (Vienna Peedee belemnite) on a scale such that 13C/12C of NBS 19 carbonate is 1.00195 times that of VPDB, and (iii) 18O/16O ratios of all substances be expressed relative to either VSMOW or VPDB on scales such that 18O/16O of SLAP is 0.9445 times that of VSMOW.
The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular-arbuscular myeorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean (Glycine max (L.) Merr.J, were grown in association with a dwarf maize (Zea mays L.) eultivar in containers which interposed a 6-cm-wide root-free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 |im) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N-sufficient soybean plants through Ni-fixation or N-fertilization on associated maize-plant growth and nutrition were compared to those of an N-deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N-fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N-defieient association. When maize was grown with nodulated soy- bean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N-fertilized treatn:ient. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N-fertilized soybean plants was more advantageous to maize than was association with the Nj-fixing ones.
In order to examine whether hyphae of VA mycorrhizal fungi may aid the transfer of symbiotically fixed nitrogen from a legume to a non-legume, the roots of berseem plants inoculated with the VAM fungus Glomus intraradices and Rhizobium leguminosarum biovar. trifolii (strain RCR 5) were separated by a 2 cm root-free zone from the roots of maize plants. A 40 um pore size nylon net allowed VAM hyphae to pass through the root-free zone but prevented root penetration. Replacement of this net by a 0.45 μm pore size membrane prevented penetration of VAM hyphae to the root-free compartment. When the berseem plants were 63 d old, the plant chambers were sealed in plastic bags to allow the roots of the plants to be exposed to a l0N2-enriched atmosphere for 5 d.
Berseem plants that were exposed to a 15N2-enriched atmosphere fixed more 15N than did berseem plants maintained under air at natural 15N abundance. The total 15N excess content of berseem was similar whether or not the mycorrhiza had access to the maize roots. Plant mass (dry weight) of maize was not affected by the mycorrhizal fungus, but total nitrogen content tended to be higher in VAM-colonized maize than in non-colonized maize. Furthermore, both atom %15N excess and 15N excess content of mycorrhizal maize were significantly increased as compared with non-mycorrhizal maize or with maize controls without berseem. The amounts of 15N transferred were small, accounting for less than 4% of the 15N in the N2-fixing plant.
In spite of the 2 cm root-free separating zone, the presence of the mycorrhizal fungus in the non-legume increased the transfer of symbiotically fixed nitrogen from berseem to maize plants that were physiologically younger. The implications of these results for nitrogen transfer from a legume to an accompanying non-legume via VAM hyphae are discussed.
The roots of most land plants are colonised by mycorrhizal fungi that provide mineral nutrients in exchange for carbon. Here, we show that mycorrhizal mycelia can also act as a conduit for signalling between plants, acting as an early warning system for herbivore attack. Insect herbivory causes systemic changes in the production of plant volatiles, particularly methyl salicylate, making bean plants, Vicia faba, repellent to aphids but attractive to aphid enemies such as parasitoids. We demonstrate that these effects can also occur in aphid-free plants but only when they are connected to aphid-infested plants via a common mycorrhizal mycelial network. This underground messaging system allows neighbouring plants to invoke herbivore defences before attack. Our findings demonstrate that common mycorrhizal mycelial networks can determine the outcome of multitrophic interactions by communicating information on herbivore attack between plants, thereby influencing the behaviour of both herbivores and their natural enemies.
The spatial association between the specially protected cacti Coryphanta durangensis, Echinocereus longisetus and Peniocereus greggii and potential nurse plants was evaluated, as was their relative position to the sun under the crown of the latter in the southern Chihuahuan Desert. The soil temperature under potential nurse plants was lower than under direct sunlight. There was more nitrogen and organic matter in the soil under Prosopis laevigata trees than in soil under direct sunlight. There were 68 plants of C. durangensis, 59 plants of E. longisetus and 157 of P. greggii. Only one individual of C. durangensis and one of E. longisetus grew outside the shade of the crown of other plants. Echinocereus longisetus was not associated with any particular species, but grew more often than expected by chance in the northern segment of the crown (i.e. the area most shaded in the afternoon). Coryphanta durangensis and P. greggii grew more often under P. laevigata than expected by chance. The effect of other plants, and P. laevigata in particular, on the facilitation of growth of protected cacti species should be considered in management plans of the Chihuahuan Desert, where mesquite (P. laevigata) is often harvested for charcoal production.
The relationship between facilitation and evolutionary ecology is poorly understood. We review five issues elucidating how the phylogenetic relatedness of species provides insight into the role of facilitation in community assembly: (a) Are the facilitative interactions more common between species that differ in a regeneration niche? (b) Are facilitative interactions more common between distantly related species? (c) Do communities governed by facilitation (rather than competition) have higher phylogenetic diversity? (d) As facilitated juvenile plants mature, do they compete with their nurses more often if they are closely related to them? (e) How does the phylogenetic signature in a community reveal ecological processes, such as succession, regeneration dynamics, indirect interactions, and coextinction cascades? The evolutionary history of lineages explains the regeneration niche of species, which ultimately determines the facilitation-competition balance and therefore community assembly and dynamics. We apply this framework to the conservation of biodiversity and propose future research avenues.
Background and aims We conducted a mesocosm study to investigate the extent to which the process of hydraulic redistribution of soil water by plant roots is affected by mycorrhizosphere disturbance. Methods We used deuterium-labeled water to track the transfer of hydraulically lifted water (HLW) from well-hydrated donor oaks (Quercus agrifolia Nee.) to drought-stressed receiver seedlings growing together in mycorrhizal or fungicide-treated mesocosms. We hypothesized that the transfer of HLW from donor to receiver plants would be enhanced in undisturbed (non-fungicide-treated) mesocosms where an intact mycorrhizal hyphal network was present.
Results Contrary to expectations, both upper soil and receiver seedlings contained significantly greater pro- portions of HLW in mesocosms where the abundance of mycorrhizal hyphal links between donor and receiver roots had been sharply reduced by fungicide application. Reduced soil hyphal density and viability likely ham- pered soil moisture retention properties in fungicide- treated mesocosms, thus leading to faster soil water depletion in upper compartments. The resulting steeper soil water potential gradient between taproot and upper compartments enhanced hydraulic redistribution in fungicide-treated mesocosms.
Compounds released by plant roots during growth can make up a high proportion of below-ground plant (BGP) carbon and nitrogen, and therefore influence soil organic matter turnover and plant nutrient availability by stimulating the soil microorganisms. The present study was conducted to examine the amount and fate of C (CdfR) and N rhizodeposits (NdfR), in this study defined as root-derived C or N present in the soil after removal of roots and root fragments, released during reproductive growth. BGP biomass of peas (Pisum sativum L.) and oats (Avena sativa L.) was successfully labelled in situ with a 13C-glucose- 15N-urea mixture under field conditions using a stem feeding method. Pea plants were labelled at the beginning of flowering and harvested 36 and 52 days after labelling at pod filling (P P) and maturity (P M), respectively. Oat plants were labelled at grain filling and harvested 42 days after labelling at maturity (O M). CdfR was 24.2% (P P), 29.6% (P M) and 30.8% (O M) of total recovered plant C. NdfR was 32.1% (P P), 36.4% (P M) and 30.0% (O M) of total plant N. Due to higher N assimilation, amounts of NdfR were four times higher in peas in comparison with oats. The results for NdfR in peas were higher than results from other studies. The C-to-N ratio of rhizodeposits was lower under peas (17.3) than under oats (41.9) at maturity. At maturity, microbial CdfR at 0-30 cm soil depth was 37% of the microbial biomass C in peas and 59% in oats. Microbial NdfR was 15% of microbial N in peas and 5% in oats. Furthermore, inorganic NdfR was 34% in peas and 9% in oats at 0-30 cm at maturity. These results show that rhizodeposits of peas provide a more easily available substrate to soil microorganisms, which are incorporated to a greater extent and turned over faster in comparison with oats. Beside the higher amounts of N released from pea roots, this process contributes to the higher N-availability for subsequent crops. © 2007 Elsevier Ltd. All rights reserved.
To eliminate possible confusion in the reporting of isotopic abundances on non-corresponding scales, the Commission on Atomic Weights and Isotopic Abundances recommended at the 37 th General Assembly at Lisbon, Portugal that (i) 2 H/ 1 H relative ratios of all substances be expressed relative to VSMOW (Vienna Standard Mean Ocean Water) on a scale such that 2 H/ 1 H of SLAP (Standard Light Antarctic Precipitation) is 0.572 times that of VSMOW, (ii) 13 C/ 12 C relative ratios of all substances be expressed relative to VPDB (Vienna Peedee belemnite) on a scale such that 13 C/ 12 C of NBS 19 carbonate is 1.00195 times that of VPDB, and (iii) 18 O/ 16 O ratios of all substances be expressed relative to either VSMOW or VPDB on scales such that 18 O/ 16 O of SLAP is 0.9445 times that of VSMOW.
Complementary beneficial effects of different arbuscular mycorrhizal fungi ( AMF ) can result in a more efficient exploitation of the soil nutrients available, thus influencing plant communities. Here, we hypothesize that plant– AMF specificity is mediated by phylogenetic constraints defining possible interactions, and that plant– AMF interaction patterns can influence plant–plant facilitation specificity.
We reanalyzed previous data describing plant–plant and plant– AMF interaction at the community level to specifically test for a phylogenetic signal on plant and AMF interactions and for a relationship between plant–plant facilitation specificity and plant species differences in their AMF associates.
Closely related AMF operational taxonomical units ( OTU s) tend to interact with the same plant species, but there is not a significant signal in the interaction through the plant phylogeny. This indicates that the similarity in the AMF associates of two plant species is independent of their phylogenetic relatedness. Interestingly, plant– AMF interactions match plant facilitation specificity, with pairs of plant species recruiting more frequently under each other tending to have different AMF associates.
An increment of AMF diversity in the rhizosphere, as a result of plant– AMF and plant–plant selectivity, is suggested as a potential driver of plant–plant facilitation. This study highlights the role of plant– AMF interactions in shaping plant community assemblages.
Relative importance of positive and negative interactions between plant species may change along disturbance and resource gradients. Positive interactions are suggested to prevail in low resource, low productivity (high stress) conditions and negative interactions in high resource availability. A dwarf shrub, mountain crowberry Empetrum nigrum ssp. hermaphroditum, is known to have allelopathic impacts on both Scots pine Pinus sylvestris and its ectomycorrhizal symbionts. We aimed to study if the outcome of Empetrum impacts on Scots pine changes along primary succession gradients on the dune shores of Bothnian Bay, in Finland, where abiotic stress gradually changes to biotic stress along the succession. We found that Empetrum may act as a facilitator despite its allelopathic effects, since the proportion of Scots pine seedlings established in Empetrum patches was higher than in patches without the shrub in early and mid succession stages, whereas patches without Empetrum were preferred in late succession. The amount of mycelial fungal biomass (ergosterol) in the soil in the vicinity of the seedling roots was higher in Empetrum patches than in patches without Empetrum and it increased along the succession gradient. Proportion of pine root tips colonised by suilloid morphotypes with abundant external mycelia and the diversity of ectomycorrhizal morphotypes were higher in mid successional stage in Empetrum patches compared to patches without Empetrum. Our results suggest that in the harsh physical conditions of the dune shore Empetrum facilitates pine seedling establishment in the early and mid stages of succession by providing mechanical and physical shelter whereas in late succession negative interactions (competition and allelopathy) between the shrub and the pine are dominating. To our knowledge we present the first finding that an ericoid mycorrhizal shrub could enhance both the performance of the ectomycorrhizal host tree and the tree's fungal symbionts.
1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant-plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant-plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.
Summary • Two-way N transfers mediated by Pisolithus sp. were examined by excluding root contact and supplying 15NH4+ or 15NO3− to 6-month-old Eucalyptus maculata or Casuarina cunninghamiana grown in two-chambered-pots separated by 37 m screens. • Mycorrhizal colonization was 35% in Eucalyptus and 66% in Casuarina (c. 29% N2-fixation). Using an environmental scanning electron microscope, living hyphae were observed to interconnect Eucalyptus and Casuarina. Biomass and N accumulation was greatest in nodulated mycorrhizal Casuarina/mycorrhizal Eucalyptus pairs, less in nonnodulated mycorrhizal Casuarina/mycorrhizal Eucalyptus pairs, and least in nonnodulated nonmycorrhizal Casuarina/nonmycorrhizal Eucalyptus pairs. • In nonnodulated mycorrhizal pairs, N transfers to Eucalyptus or to Casuarina were similar (2.4–4.1 mg per plant in either direction) and were 2.6–4.0 times greater than in nonnodulated nonmycorrhizal pairs. In nodulated mycorrhizal pairs, N transfers were greater to Eucalyptus (5–7 times) and to Casuarina (12–18 times) than in nonnodulated mycorrhizal pairs. Net transfer to Eucalyptus or to Casuarina was low in both nonnodulated nonmycorrhizal (Casuarina was 26.0 mg per plant. • The amount and direction of two-way mycorrhiza-mediated N transfer was increased by the presence of Pisolithus sp. and Frankia, resulting in a net N transfer from low-N-demanding Eucalyptus to high-N-demanding Casuarina. ©New Phytologist (2004) doi: 10.1111/j.1469-8137.2004.01137.x