Search

Summary Elton's biotic resistance hypothesis predicts that biodiversity can resist the establishment of invasive plants. However, whether and how within‐species diversity mediates the impacts of successfully established invaders is poorly understood, particularly in the face of climate change. We used an experimental system to test the effect of intraspecific diversity of a native foundation species, Scirpus mariqueter, on the soil‐legacy impacts of a global plant invader, Spartina alterniflora, under well‐watered and drought conditions. We found that more diverse populations of the native plant buffered against the negative soil‐legacy impacts of the invader on the native plant. This intraspecific diversity effect was due to a complementarity effect triggered by invader‐shaped soil biota, and emerged in both well‐watered and drought conditions. Compared with the previous finding that intraspecific diversity of the native plant can reduce the performance of the invader through soil biotic feedbacks, this study provides further evidence that it helps to mitigate the negative soil‐derived impacts of the invader. These findings together emphasize the need for management measures that promote and restore native intraspecific diversity in a changing world. [ABSTRACT FROM AUTHOR]

Plant community ecology guides restoration of degraded lands, yet seed‐based restorations sometimes fail or result in unpredictable outcomes, necessitating a better understanding of community trajectory and stability. Western yarrow (Achillea millefolium) declined suddenly in two separate restoration projects after initial high relative abundance. To assess the potential role of soil pathogens, we surveyed plant and soil fungal communities in these restorations, and used an 8‐year‐old field experiment that crossed yarrow planted in varying densities with a fungicide treatment. Two greenhouse experiments then evaluated whether the suppressive effect in yarrow soil spread to native species used in restoration. Lower yarrow cover in a restoration project 5 years compared to 3 years after seeding coincided with higher relative abundance of fungal taxa that can cause disease, particularly Crown‐rot fungi (Paraphoma spp.). Paraphoma increased over time in experimental plots and coincided with yarrow decline. Decline onset was density‐dependent, occurring faster in plant communities where yarrow density was higher. Fungicide applications altered fungal pathogen communities and promoted yarrow cover relative to control plots. In the greenhouse, yarrow grew larger with fungicide, consistent with suppression of fungal pathogens. However, biomass of natives grown in yarrow‐conditioned soil was not affected by fungicides, suggesting pathogens did not spread. The rapid establishment and competitive nature of yarrow, followed by pathogen‐induced decline, make it an attractive early transitional "bridge species," so long as its pathogens are species‐specific. Our results suggest negative plant‐soil feedback can drive rapid decline of individual species, and considering plant–soil feedback could improve restoration predictability. [ABSTRACT FROM AUTHOR]

Litter decomposition is not fully explained by the general triangle of climate, litter quality and soil decomposers. Therefore, other theoretical frameworks, such as Home-Field Advantage (HFA), have emerged to explain the remaining variation of decomposition. HFA states that litter decomposes faster in their site of origin (home) than far from it (away). However, there are no consistent patterns of HFA and this can varies depending the ecosystem and plant species analyzed. One of the most variable ecosystems in terms of species biodiversity turnover, topography, and soil conditions are the Upper Andean Tropical Forests (UATF), but to date there is no study testing HFA in this ecosystem. Here, HFA was tested through a reciprocal litterbag translocation field experiment across different UATF. The experiment comprised 2520 litterbags placed in 14 20 x 20 m plots that belonged to four sites to analyze decomposition of 15 plant species for 18 months. Of these 15 species, seven were present at only one site. The mean decomposition was calculated for all 15 species to determine the relative decomposition at each site and the decomposition of the seven species at home and away sites was analyzed through two-way ANOVA (sites x species) and linear mixed models. I contrasted environmental charcteristics between sites including litter depth, slope, leaf area index, canopy openness, and microclimatic variables. The results showed that the pattern of decomposition was always the same, no matter the origin of the species and the decomposition period. Microclimate, litter depth, and slope varied between sites, yet these differences were not enough to influence affinity effects of decomposition, as relative decay rates were similar between home and away sites. Overall, no HFA was found in UATF possibly because: (i) strong environmental filters along montane forests homogenize decomposer communities; (ii) high diversity in litters drive decomposers with high ability to degrade different organic compounds; (iii) little adaptation of decomposers to recurrent litter as they respond mainly to changes in litter quality. These results imply that changes in species composition by current anthropogenic pressures could have profound impacts on carbon cycle and nutrient fluxes depending on the identity of species arriving in UATF. [ABSTRACT FROM AUTHOR]

Drought may impact plant–soil biotic interactions in ways that modify aboveground herbivore performance, but the outcomes of such biotic interactions under future climate are not yet clear. We performed a growth chamber experiment to assess how long‐term, drought‐driven changes in belowground communities influence plant growth and herbivore performance using a plant–soil feedback experimental framework. We focussed on two common pasture legumes—lucerne, Medicago sativa L., and white clover, Trifolium repens L. (both Fabaceae)—and foliar herbivores—cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), and two‐spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Soil was collected from a field facility where rainfall had been manipulated for 6 years, focussing on treatments representing ambient rainfall and prolonged drought (50% reduction relative to ambient), to consider the effects of biological legacies mediated by the prolonged drought. All soils were sterilized and re‐inoculated to establish the respective home (i.e. where a given plant is cultivated in its own soil) and away (i.e. where a given plant is cultivated in another species' soil) treatments in addition to a sterile control. We found that the relative growth rate (RGR) and relative consumption of larvae were significantly lower on lucerne grown in soil with ambient rainfall legacies conditioned by white clover. Conversely, the RGR of insect larvae was lower on white clover grown in soil with prolonged drought legacies conditioned by lucerne. Two‐spotted spider mite populations and area damage (mm2) were significantly reduced on white clover grown in lucerne‐conditioned soil in drought legacies. The higher number of nodules found on white clover in lucerne‐conditioned soil suggests that root–rhizobia associations may have reduced foliar herbivore performance. Our study provides evidence that foliar herbivores are affected by plant–soil biotic interactions and that prolonged drought may influence aboveground–belowground linkages with potential broader ecosystem impacts. [ABSTRACT FROM AUTHOR]

Differences between arbuscular (AM) and ectomycorrhizal (EcM) trees strongly influence forest ecosystem processes, in part through their impact on saprotrophic fungal communities. Ericoid mycorrhizal (ErM) shrubs likely also impact saprotrophic communities given that they can shape nutrient cycling by slowing decomposition rates and intensifying nitrogen limitation. We investigated the depth distributions of saprotrophic and EcM fungal communities in paired subplots with and without a common understory ErM shrub, mountain laurel (Kalmia latifolia L.), across an AM to EcM tree dominance gradient in a temperate forest by analyzing soils from the organic, upper mineral (0–10 cm), and lower mineral (cumulative depth of 30 cm) horizons. The presence of K. latifolia was strongly associated with the taxonomic and functional composition of saprotrophic and EcM communities. Saprotrophic richness was consistently lower in the Oa horizon when this ErM shrub species was present. However, in AM tree-dominated plots, the presence of the ErM shrub was associated with a higher relative abundance of saprotrophs. Given that EcM trees suppress both the diversity and relative abundance of saprotrophic communities, our results suggest that separate consideration of ErM shrubs and EcM trees may be necessary when assessing the impacts of plant mycorrhizal associations on belowground communities. [ABSTRACT FROM AUTHOR]

Species traits may determine plant interactions along with soil microbiome, further shaping plant–soil feedbacks (PSFs). However, how plant traits modulate PSFs and, consequently, the dominance of plant functional groups remains unclear. We used a combination of field surveys and a two‐phase PSF experiment to investigate whether forbs and graminoids differed in PSFs and in their trait–PSF associations. When grown in forb‐conditioned soils, forbs experienced stronger negative feedbacks, while graminoids experienced positive feedbacks. Graminoid‐conditioned soil resulted in neutral PSFs for both functional types. Forbs with thin roots and small seeds showed more‐negative PSFs than those with thick roots and large seeds. Conversely, graminoids with acquisitive root and leaf traits (i.e., thin roots and thin leaves) demonstrated greater positive PSFs than graminoids with thick roots and tough leaves. By distinguishing overall and soil biota‐mediated PSFs, we found that the associations between plant traits and PSFs within both functional groups were mainly mediated by soil biota. A simulation model demonstrated that such differences in PSFs could lead to a dominance of graminoids over forbs in natural plant communities, which might explain why graminoids dominate in grasslands. Our study provides new insights into the differentiation and adaptation of plant life‐history strategies under selection pressures imposed by soil biota. [ABSTRACT FROM AUTHOR]

Although native species diversity is frequently reported to enhance invasion resistance, within‐species diversity of native plants can also moderate invasions. While the positive diversity–invasion resistance relationship is often attributed to competition, indirect effects mediated through plant–soil feedbacks can also influence the relationship. We manipulated the genotypic diversity of an endemic species, Scirpus mariqueter, and evaluated the effects of abiotic versus biotic feedbacks on the performance of a global invader, Spartina alterniflora. We found that invader performance on live soils decreased non‐additively with genotypic diversity of the native plant that trained the soils, but this reversed when soils were sterilized to eliminate feedbacks through soil biota. The influence of soil biota on the feedback was primarily associated with increased levels of microbial biomass and fungal diversity in soils trained by multiple‐genotype populations. Our findings highlight the importance of plant–soil feedbacks mediating the positive relationship between genotypic diversity and invasion resistance. [ABSTRACT FROM AUTHOR]

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Plant–microbial interactions in soils are considered to play a central role in regulating biodiversity in many global ecosystems. However, studies on plant–soil feedbacks (PSFs) and how these affect forest stand patterns in boreal regions are rare.We conducted a fully reciprocal PSF glasshouse experiment using four boreal tree species. Alnus glutinosa, Betula pendula, Picea abies and Pinus sylvestris seedlings were grown under controlled conditions in sterilised soil with or without soil inoculum collected under mature trees of each of the four species. Bacterial, fungal and oomycete communities in the rhizosphere were investigated using metabarcoding and correlated with differences in plant biomass.Alder grew best in conspecific soil, whereas birch grew equally well in all soil types. Pine and spruce grew best in heterospecific soil, particularly in soil from their successional predecessor. Ectomycorrhizal fungi (EMF) enhanced the growth of most seedlings, and Actinomycetota supported alder and birch growth and fungal plant pathogens hampered pine growth. Increased growth was linked to the ability of trees to recruit specific EMF and root‐associated fungi in heterospecific soils.Synthesis. This study experimentally examines the influence of root‐associated microbiota on the growth of boreal tree species. The observed plant–soil feedbacks mirror the successional patterns found in boreal forests, suggesting a possible contribution of soil microbiota to the successional progression. Species‐specific ectomycorrhizal fungi and a few bacteria rather than fungal plant pathogens or oomycetes seem to drive the feedbacks by promoting seedling growth in heterospecific soils. [ABSTRACT FROM AUTHOR]

Plant-soil feedback (PSF) processes impact plant productivity and ecosystem function, but they are poorly understood because PSFs vary significantly with plant and soil type, plant growth stage, and environmental conditions. Controlled greenhouse studies are essential to unravel the mechanisms associating PSFs with plant productivity; however, successful implementation of these controlled experiments is constrained by our understanding of the persistence of the soil microbiome during the transition from field to greenhouse. This study evaluates the preservation potential of a field soil microbiome when stored in the laboratory under field temperature and moisture levels. Soil microbial diversity, taxonomic composition, and functional potential were evaluated via amplicon sequencing at the start of storage (W0), week 3 (W3), week 6 (W6), and week 9 (W9) to determine the effect of storage time on soil microbiome integrity. Though microbial richness remained stable, Shannon diversity indices decreased significantly at W6 for bacteria/archaea and W3 for fungi. Bacterial/archaeal community composition also remained stable, whereas the fungal community changed significantly during the first 3 weeks. Functional predictions revealed increased capacity for chemoheterotrophy for bacteria/archaea and decreased relative proportions of arbuscular mycorrhizal and ectomycorrhizal fungi. We show that preservation of the field soil microbiome must be a fundamental component of experimental design. Either greenhouse experiments should be initiated within 3 weeks of field soil collection, or a preliminary incubation study should be conducted to determine the time and storage conditions required to sustain the integrity of the specific field soil microbiome being studied. [ABSTRACT FROM AUTHOR]

As climate change increases fire frequency in Mediterranean‐type shrublands, it is essential to understand the links between common postfire plant assemblages and soil nitrogen (N) and carbon (C) cycling during succession. In California chaparral, periodic fire removes shrub cover, deposits ammonium (NH4+‐N) on soils, and allows herbaceous assemblages to dominate for 3–5 years. Herbs influence soil biogeochemistry through several mechanisms, including nutrient uptake, litter decomposition, and rhizodeposition. Controlled experimental removal of select plant groups from wild assemblages can demonstrate interactions between plant groups and how plant traits influence belowground processes. In a two‐year herb‐removal experiment, we investigated the impact of N‐fixing and non‐N‐fixing herbs on soil N and C cycling. Treatments were (1) all herbs, (2) only non‐N‐fixing species, (3) only N‐fixing species, and (4) no herbs. In high‐N environments, N‐fixers were predicted to compete poorly against non‐N‐fixing neighbors. N‐fixers doubled in abundance when non‐N‐fixers were removed, but non‐N‐fixers were unaffected by N‐fixer removal. Two years after fire, no‐herbs plots had the lowest soil microbial respiration rates, and total accumulated C and N were lower than all‐herb plots. Two treatments, no‐herb and N‐fixer plots, had elevated mineral N concentrations, net N mineralization, and net nitrification in the second year of the experiment. Our findings underscore the importance of fire‐following herbs for postfire N retention and organic matter accumulation. A combination of both N‐fixing and non‐N‐fixing herbs maximized total soil C and N, although the accumulation of TC and TN in all‐herb plots was not significantly higher than in non‐N‐fixer plots. Results demonstrated the key role of non‐N‐fixing herbs in accumulating soil C and herbaceous communities for retaining N. Elevated soil nutrient availability two years postfire may contribute to the long‐term recovery of shrubs, even after herbs are no longer dominant. Future investigations should also consider the magnitude of soil microbial N retention in plots with different herb functional groups, along with the species‐specific contribution of non‐N‐fixing herbs to postfire C and N cycling. [ABSTRACT FROM AUTHOR]

Soil biota have strong effects on plants, but we have a poor understanding of how plant chemistry might modify these effects. We examined the effect of soil biota associated with an exotic invasive tree, Prosopis juliflora, versus that associated with native species, from seven sites across India on conspecifics and two other plant species. We then measured changes in species‐specific soil biota effects (identified as plant–soil feedbacks, PSFs) when leaf leachate from P. juliflora or from native plant species was added to soil containing respective live and sterile soil inoculum.We quantified the amino acid L‐tryptophan from leaf leachate of P. juliflora, Leucaena leucocephala (another invader), and two native species. We also tested effects of P. juliflora or native species soil inoculum amendment of tryptophan on P. juliflora, P. cineraria and L. leucocephala across seven sites. We then quantified the microbially metabolized derivatives of tryptophan, phytohormone indole‐3‐acetic acid (IAA) and intermediates after adding tryptophan into P. juliflora and native soils.Soil biota associated with P. juliflora generated positive effects on conspecifics and L. leucocephala, but negative effects on the native congener P. cineraria. When P. juliflora leaf leachate was added to soil with live P. juliflora inoculum, PSFs became more positive for P. juliflora and other species, compared to leaf leachate amended with sterile soil inoculum. Native leaf leachate interacted weakly with soil biota to impact biomass of conspecifics and heterospecifics.There was roughly 10× more tryptophan in the leaf leachate of P. juliflora than in the leaf leachate of other species. Tryptophan generally increased positive PSFs associated with P. juliflora relative to soil biota associated with other plant species. When tryptophan was added to live P. juliflora soil, IAA and its intermediates were produced at five of seven sites, and at four of these sites soil biota from P. juliflora had positive PSFs.Synthesis. These results provide the first experimental evidence that a chemical leached from the leaves of an invader regulates PSFs. Our results indicate that canopy effects and PSFs, which are usually studied independently, can interact in ways that strongly affect conspecifics and neighbouring species. [ABSTRACT FROM AUTHOR]

Recent studies have shown the potential for negative plant–soil feedbacks (PSFs) to promote stable coexistence, but have not quantified the stabilizing effect relative to other coexistence mechanisms. We conducted a field experiment to test the role of PSFs in stabilizing coexistence among four dominant sagebrush steppe species that appear to coexist stably, based on previous work with observational data and models. We then integrated the effects of PSF treatments on focal species across germination, survival, and first‐year growth. To contribute to stable coexistence, soil microbes should have host‐specific effects that result in negative feedbacks. Over two replicated growing seasons, our experiments consistently showed that soil microbes have negative effects on plant growth, but these effects were rarely host‐specific. The uncommon host‐specific effects were mostly positive at the germination stage, and negative for growth. Integrated effects of PSF across early life‐stage vital rates showed that PSF‐mediated self‐limitation occasionally had large effects on projected plant biomass, but occurred inconsistently between years. Our results suggest that while microbially‐mediated PSF may not be a common mechanism of coexistence in this community, it may still affect the relative abundance of dominant plant species via changes in host fitness. Our work also serves as a blueprint for future investigations that aim to identify underlying processes and test alternative mechanisms to explain important patterns in community ecology. [ABSTRACT FROM AUTHOR]

Invasions at high latitudes are recognized as an emerging threat to native biodiversity, but non-native plants still are scarce in northern Canada. One factor potentially inhibiting further invasions may be below-ground interactions; in particular, it is unclear whether interactions with soil biota are likely to help or hinder the spread of new species into often challenging northern soils. In the Canadian subarctic, the non-native plant Linaria vulgaris has invaded human-disturbed soils in the town of Churchill, Manitoba (58.8°N) but for decades has failed to spread into natural communities. One explanation for this stasis might be greater resistance by soil communities in uninvaded areas relative to areas where this plant is established; however, no local evidence for plant-soil feedbacks exists. In one of the first papers to test the potential role of plant-soil feedbacks in an invasion at high latitudes, we planted L. vulgaris in soil serially inoculated with live and sterilized field-collected soil sampled from invaded or uninvaded sites, and measured plant performance (biomass) over three iterations. We also conducted soil chemical analyses to determine whether pH, and carbon, nitrogen, and phosphorous contents differ between invaded and uninvaded areas. There was no initial difference in biomass between inoculation treatments in the first two iterations. However, by iteration 3, we found that sterilization significantly increased L. vulgaris biomass in invaded soils, indicating feedback becomes negative in invaded soils compared to uninvaded soils. Soil chemistry did not differ significantly between invaded and uninvaded soils, though there was a tendency for invaded soils to contain more carbon and nitrogen. These results do not support the hypothesis that L. vulgaris is absent from uncolonized sites because soil communities resist invasion. Instead, they provide evidence that L. vulgaris is inhibited by plant-soil feedbacks in invaded soils, while feedbacks in native-dominated soils are not a barrier to further local spread. Thus, explanations for the restriction of this species must lie elsewhere. [ABSTRACT FROM AUTHOR]

Although plant–soil feedbacks (interactions between plants and soils, often mediated by soil microbes, abbreviated as PSFs) are widely known to influence patterns of plant diversity at local and landscape scales, these interactions are rarely examined in the context of important environmental factors. Resolving the roles of environmental factors is important because the environmental context may alter PSF patterns by modifying the strength or even direction of PSFs for certain species. One important environmental factor that is increasing in scale and frequency with climate change is fire, though the influence of fire on PSFs remains essentially unexamined. By changing microbial community composition, fire may alter the microbes available to colonize the roots of plants and thus seedling growth post‐fire. This has potential to change the strength and/or direction of PSFs, depending on how such changes in microbial community composition occur and the plant species with which the microbes interact. We examined how a recent fire altered PSFs of two leguminous, nitrogen‐fixing tree species in Hawaiʻi. For both species, growing in conspecific soil resulted in higher plant performance (as measured by biomass production) than growing in heterospecific soil. This pattern was mediated by nodule formation, an important process for growth for legume species. Fire weakened PSFs for these species and therefore pairwise PSFs, which were significant in unburned soils, but were nonsignificant in burned soils. Theory suggests that positive PSFs such as those found in unburned sites would reinforce the dominance of species where they are locally dominant. The change in pairwise PSFs with burn status shows PSF‐mediated dominance might diminish after fire. Our results demonstrate that fire can modify PSFs by weakening the legume‐rhizobia symbiosis, which may alter local competitive dynamics between two canopy dominant tree species. These findings illustrate the importance of considering environmental context when evaluating the role of PSFs for plants. [ABSTRACT FROM AUTHOR]

Summary: Plant–soil feedbacks (PSFs) are an important mechanism of species coexistence in forest communities. However, evidence remains limited for how light availability regulates PSFs in species with different shade tolerance via changes in plant–microbial interactions.Here we tested in a glasshouse experiment how PSFs changed as a function of light availability and tree shade tolerance. Soil bacterial and fungal communities were profiled using the 16S rRNA and ITS2 gene sequencing, respectively.Under low light, individual PSFs were positively related to shade tolerance, while the least shade‐tolerant species produced the most positive PSFs under high light. Pairwise PSFs between species with contrasting shade tolerance were strongly positive under high light but negative under low light, thereby promoting the dominance of less shade‐tolerant species in forest gaps and species coexistence under closed canopy, respectively. Under high light, PSFs were related to soil microbial composition and diversity, with the relative abundance of arbuscular mycorrhizal fungi being the primary driver of PSFs. Under low light, none of soil microbial properties were significantly related to PSFs.These findings indicate PSFs and plant shade tolerance interact to promote species coexistence and improve our understanding of how soil microbes contribute to variation in PSFs. [ABSTRACT FROM AUTHOR]

Livestock grazing is an important element in ecosystem regulation since it may affect essential ecosystem functions, such as nutrient acquisition, organic matter decomposition, or litter accumulation in the soil. Overgrazing can threaten the conservation of ecosystems through excessive defoliation of plants or trampling. On the contrary, moderate grazing can have benefits on ecosystem dynamics by favoring nutrient cycling or the soil microbial activity. The aim of this study was to analyze these effects in a semi-arid Mediterranean shrubland located in NE Spain. We established six study sites including three grazing intensities, where we sampled vegetation biomass and soil properties: nitrogen content, microbial biomass, water infiltration capacity, porosity, and gypsum content. These parameters were included in a plant-soil interaction model tested through Structural Equation Modeling. Grazing had a direct negative effect on plant biomass (p < 0.01) and water infiltration capacity (p < 0.05) affecting soil nitrogen content (p < 0.001) and microbial biomass (p < 0.5), respectively. Infiltration capacity and porosity were primary drivers of plant biomass (p < 0.05, both cases), and plant biomass was the main contributor to the soil nitrogen pool. Microbial biomass was dependent on infiltration capacity (p < 0.05), porosity (p < 0.01), and nitrogen (p < 0.01). Grazing directly or indirectly affected the functioning of the ecosystem through effects on plant and soil attributes, which may result in changes in plant growth, litter decomposition, or plant nutrient acquisition. This study revealed that moderate grazing can maintain optimal ecosystem features and prevent ecosystem degradation. [ABSTRACT FROM AUTHOR]

Plant-soil feedbacks have been recognised as playing a key role in a range of ecological processes, including succession, invasion, species coexistence and population dynamics. However, there is substantial variation between species in the strength of plant-soil feedbacks and predicting this variation remains challenging. Here, we propose an original concept to predict the outcome of plant-soil feedbacks. We hypothesize that plants with different combinations of root traits culture different proportions of pathogens and mutualists in their soils and that this contributes to differences in performance between home soils (cultured by conspecifics) versus away soils (cultured by heterospecifics). We use the recently described root economics space, which identifies two gradients in root traits. A conservation gradient distinguishes fast vs. slow species, and from growth defence theory we predict that these species culture different amounts of pathogens in their soils. A collaboration gradient distinguishes species that associate with mycorrhizae to outsource soil nutrient acquisition vs. those which use a "do it yourself" strategy and capture nutrients without relying strongly on mycorrhizae. We provide a framework, which predicts that the strength and direction of the biotic feedback between a pair of species is determined by the dissimilarity between them along each axis of the root economics space. We then use data from two case studies to show how to apply the framework, by analysing the response of plant-soil feedbacks to measures of distance and position along each axis and find some support for our predictions. Finally, we highlight further areas where our framework could be developed and propose study designs that would help to fill current research gaps. [ABSTRACT FROM AUTHOR]

Inoculating soils with microbiota that benefit the germination and growth of endangered plant species could improve their revegetation success and conservation status. While ecosystem degradation can disrupt beneficial plant–soil‐microbial interactions, the prospect of reintroducing native plant‐associated soil microbiota during revegetation could help to restore these important ecological links and assist the recovery of key species. We address the role of soil microbiota on germination and seedling fitness traits of the endangered Acacia whibleyana (Fabaceae) through a 17‐week greenhouse experiment. Soil treatments included local soil, potting medium, three inoculation ratios (3:1, 1:1, 1:3 local soil: potting medium), sterilized local soil and sterilized potting medium. Soil sterilization reduced the time to first seed germination, indicating a role of soil microbiota on germination. The 1:1 whole soil inoculation saw reduced germination rates compared with either pure local or potting‐medium treatments, and the slower germination times observed in live soils confirmed the strong influence of soil microbiota on the timing of germination. We report evidence that poor inoculation strategies can adversely impact germination of this endangered Acacia. Furthermore, our findings suggest that careful assessment of microbiota associated with A. whibleyana could help to improve germination and recruitment during its revegetation and conservation management. Ecosystem degradation can disrupt beneficial plant–soil‐microbial interactions, but reintroducing native plant‐associated soil microbiota during revegetation could potentially help to restore these important ecological links and assist the recovery of key species. We address the role of soil microbiota on germination and seedling fitness traits of the endangered Acacia whibleyana (Fabaceae) through a 17 week greenhouse experiment. We report evidence that poor inoculation strategies can adversely impact germination of this endangered Acacia, and our findings suggest that careful assessment of microbiota associated with A. whibleyana could help to improve germination and recruitment during its revegetation and conservation management. [ABSTRACT FROM AUTHOR]

Summary: Feedbacks between plants and soil microbes form a keystone to terrestrial community and ecosystem dynamics. Recent advances in dissecting the spatial and temporal dynamics of plant–soil feedbacks (PSFs) have challenged longstanding assumptions of spatially well‐mixed microbial communities and exceedingly fast microbial assembly dynamics relative to plant lifespans. Instead, PSFs emerge from interactions that are inherently mismatched in spatial and temporal scales, and explicitly considering these spatial and temporal dynamics is crucial to understanding the contribution of PSFs to foundational ecological patterns. I propose a synthetic spatiotemporal framework for future research that pairs experimental and modeling approaches grounded in mechanism to improve predictability and generalizability of PSFs. [ABSTRACT FROM AUTHOR]

Abstract As climate change increases fire frequency in Mediterranean‐type shrublands, it is essential to understand the links between common postfire plant assemblages and soil nitrogen (N) and carbon (C) cycling during succession. In California chaparral, periodic fire removes shrub cover, deposits ammonium (NH4+‐N) on soils, and allows herbaceous assemblages to dominate for 3–5 years. Herbs influence soil biogeochemistry through several mechanisms, including nutrient uptake, litter decomposition, and rhizodeposition. Controlled experimental removal of select plant groups from wild assemblages can demonstrate interactions between plant groups and how plant traits influence belowground processes. In a two‐year herb‐removal experiment, we investigated the impact of N‐fixing and non‐N‐fixing herbs on soil N and C cycling. Treatments were (1) all herbs, (2) only non‐N‐fixing species, (3) only N‐fixing species, and (4) no herbs. In high‐N environments, N‐fixers were predicted to compete poorly against non‐N‐fixing neighbors. N‐fixers doubled in abundance when non‐N‐fixers were removed, but non‐N‐fixers were unaffected by N‐fixer removal. Two years after fire, no‐herbs plots had the lowest soil microbial respiration rates, and total accumulated C and N were lower than all‐herb plots. Two treatments, no‐herb and N‐fixer plots, had elevated mineral N concentrations, net N mineralization, and net nitrification in the second year of the experiment. Our findings underscore the importance of fire‐following herbs for postfire N retention and organic matter accumulation. A combination of both N‐fixing and non‐N‐fixing herbs maximized total soil C and N, although the accumulation of TC and TN in all‐herb plots was not significantly higher than in non‐N‐fixer plots. Results demonstrated the key role of non‐N‐fixing herbs in accumulating soil C and herbaceous communities for retaining N. Elevated soil nutrient availability two years postfire may contribute to the long‐term recovery of shrubs, even after herbs are no longer dominant. Future investigations should also consider the magnitude of soil microbial N retention in plots with different herb functional groups, along with the species‐specific contribution of non‐N‐fixing herbs to postfire C and N cycling.

Plant-soil feedback (PSF) processes impact plant productivity and ecosystem function, but they are poorly understood because PSFs vary significantly with plant and soil type, plant growth stage, and environmental conditions. Controlled greenhouse studies are essential to unravel the mechanisms associating PSFs with plant productivity; however, successful implementation of these controlled experiments is constrained by our understanding of the persistence of the soil microbiome during the transition from field to greenhouse. This study evaluates the preservation potential of a field soil microbiome when stored in the laboratory under field temperature and moisture levels. Soil microbial diversity, taxonomic composition, and functional potential were evaluated via amplicon sequencing at the start of storage (W0), week 3 (W3), week 6 (W6), and week 9 (W9) to determine the effect of storage time on soil microbiome integrity. Though microbial richness remained stable, Shannon diversity indices decreased significantly at W6 for bacteria/archaea and W3 for fungi. Bacterial/archaeal community composition also remained stable, whereas the fungal community changed significantly during the first 3 weeks. Functional predictions revealed increased capacity for chemoheterotrophy for bacteria/archaea and decreased relative proportions of arbuscular mycorrhizal and ectomycorrhizal fungi. We show that preservation of the field soil microbiome must be a fundamental component of experimental design. Either greenhouse experiments should be initiated within 3 weeks of field soil collection, or a preliminary incubation study should be conducted to determine the time and storage conditions required to sustain the integrity of the specific field soil microbiome being studied.

The persistence of mutualisms is paradoxical, as there are fitness incentives for exploitation. This is particularly true for plant-microbe mutualisms like arbuscular mycorrhizae (AM), which are promiscuously horizontally transmitted. Preferential allocation by hosts to the best mutualist can stabilize horizontal mutualisms; however, preferential allocation is imperfect, with its fidelity likely depending on the spatial structure of symbionts in plant roots. In this study we tested AM mutualisms' dependence on two dimensions of spatial structure—the initial spatial association of fungi and the ease of fungal dispersal—through three complementary experiments. We found that fitness of the beneficial AM fungus increased when fungi were initially separate, while initial spatial mixing benefited the fitness of the nonbeneficial fungus. These effects were strongest when dispersal was limited and hosts could discriminate. Additionally, we found that changes in AM fungal proportional abundance induced by spatial structure in roots of a preferentially allocating host produced positive feedbacks on plant growth, showing that interactions between spatial structure and host choice can determine the direction of plant-soil feedbacks. Our results suggest that symbiont spatial structure within plant roots may act as an important modifier of plant preferential allocation and the dynamics of mycorrhizal mutualisms, with potentially cascading effects on plant-plant interactions. [ABSTRACT FROM AUTHOR]

These groups did not match the I Z i -score values calculated for each pine species: some pine species predicted to be invasive based on their I Z i -score grouped with plantation and introduced EMF, while some pine species predicted to be non-invasive based on their I Z i -score grouped with invasive EMF (both early- and late-successional) (Fig. Keywords: belowground microbes; ectomycorrhizas; invasive fungi; Pinus; plant invasions; plant-soil feedbacks EN belowground microbes ectomycorrhizas invasive fungi Pinus plant invasions plant-soil feedbacks 16 21 6 12/08/22 20230101 NES 230101 Symbiotic soil microbes can facilitate plant invasions, yet it is unclear whether the invasive capacity of plants can be explained by the invasiveness of their microbial symbionts. After compiling a global dataset on associations between non-native invasive pine trees and ectomycorrhizal fungi (EMF), we found that the interaction with invasive EMF is an important predictor of pine invasion success that acts in concert with aboveground plant traits, questioning the way we currently predict plant invasions. To test the hypothesis that invasive pine species are more frequently associated with invasive EMF, we performed a principal coordinates analysis (PCoA), based on the dissimilarity among pine species in the frequency of association with each EMF species. [Extracted from the article]

Summary: Plant–soil feedbacks (PSFs) underlying grassland plant richness and productivity are typically coupled with nutrient availability; however, we lack understanding of how restoration measures to increase plant diversity might affect PSFs. We examined the roles of sward disturbance, seed addition and land‐use intensity (LUI) on PSFs.We conducted a disturbance and seed addition experiment in 10 grasslands along a LUI gradient and characterized plant biomass and richness, soil microbial biomass, community composition and enzyme activities.Greater plant biomass at high LUI was related to a decrease in the fungal to bacterial ratios, indicating highly productive grasslands to be dominated by bacteria. Lower enzyme activity per microbial biomass at high plant species richness indicated a slower carbon (C) cycling. The relative abundance of fungal saprotrophs decreased, while pathogens increased with LUI and disturbance. Both fungal guilds were negatively associated with plant richness, indicating the mechanisms underlying PSFs depended on LUI.We show that LUI and disturbance affect fungal functional composition, which may feedback on plant species richness by impeding the establishment of pathogen‐sensitive species. Therefore, we highlight the need to integrate LUI including its effects on PSFs when planning for practices that aim to optimize plant diversity and productivity. [ABSTRACT FROM AUTHOR]

Nutrient cycling in forest ecosystems can be sensitive to disturbances that change the availability of one nutrient relative to others, altering the synchrony in nutrient cycles that is expected to develop in undisturbed systems. We asked whether the relative availabilities of nitrogen (N) and phosphorus (P) differ with forest successional age after harvest, and tested effects of adding one nutrient on availability and recycling of the other, in a factorial nitrogen (N) × phosphorus (P) fertilization study in multiple early- and mid-successional and mature northern hardwood forest stands in central NH, USA. We did not find effects of forest age on resin-available N:P ratios, which varied widely among successional forest stands and were related to net N mineralization potentials in the forest floor of each stand. P addition suppressed resin-N availability by 31 % and lowered litterfall N recycling by 10 %, but we detected no effects on net N mineralization potentials. P addition also increased nitrification potentials in the organic horizon by up to 60 %, mostly in combination with added N. The effects of added N depended on P; lower resin-P in mature stands and lower litterfall P recycling in stands of all ages were detected only when P was added with N. We conclude that P limitation influences N recycling across forest age classes in these northern hardwoods, with some indication of stronger effects in successional stands. However, net N mineralization potentials better predicted the resin-N response to added P than did stand age. Our results suggest that alleviating P limitation promotes N limitation over time, especially in more rapidly growing successional forests, by increasing biotic demand for N, reducing its recycling in litterfall, and potentially by reducing net N mineralization. • Resin-available N:P varied in relation to net N mineralization and not forest age. • Resin-available N and litterfall N recycling declined in response to added P. • Litterfall P recycling declined in response to N only when added with P. • P limitation influences N and P cycling in these northern hardwoods. [ABSTRACT FROM AUTHOR]

Plant–soil feedbacks (PSF) play an important role in determining plant community structure and dynamics. However, previous studies have provided mixed results for the relationship between PSF and plant landscape abundance (i.e. abundance across local communities). This may reflect the mediation of climate factors on PSF. Here, we tested how PSF of tree species varied with local abundances by growing seedlings in conspecific versus heterospecific soil and how simulated drought altered PSF–plant abundance relationships. Six tree species were selected and half of the seedlings were grown under ambient moisture conditions, while the others experienced a 2‐month period of drought following 3‐months of growth under ambient moisture conditions. Fungal communities in the rhizosphere soil were analysed using DNA amplicon sequencing to link shifts in soil fungi to the observed PSF. We found that drought reduced negative PSF for all plant species except one species (Lithocarpus lohangwu). In the drought treatments, PSF were positively correlated with the relative abundance of total putative pathogens, but negatively correlated with the proportion of unique pathogens (those pathogens that were present in conspecific soil rather than heterospecific soil, thereby potentially species‐specific). In addition, we found that PSF only significantly predicted plant relative abundance in the drought treatment, indicating that abiotic stress made PSF a stronger predictor of plant landscape abundance. This finding also implies that future extreme drought events could promote the dominance of the abundant plant species, thereby leading to the loss of biodiversity. Collectively, our results provide evidence for microbial mechanisms of PSF and suggest that accounting for abiotic stress can make PSF a stronger predictor of plant landscape abundance due to the omnipresence of stress under natural conditions. [ABSTRACT FROM AUTHOR]

Changes in soil chemistry after invasion by bracken (Pteridium aquilinum) have been studied in heathlands, but comparable studies in meadows are lacking. We investigated if bracken invasion into P-deficient meadows alters the soil nutrient-resource pool, as well as the mechanisms behind it linked to soil processes and bracken nutrition. Furthermore, we investigated how community composition responds to differences in soil chemistry before and after the invasion. Soil and plant material sampling, along with vegetation survey, were performed during bracken peak biomass. Data analyses included analysis of variance and canonical correspondence analysis (CCA). Bracken invasion increased soil P availability, soil organic C concentration, as well as C:N, C:S and N:S ratios, while decreasing Fe and Co concentrations. Bracken pinnae were rich in P, and its rhizomes were rich in K, whereas N:P of pinnae and rhizomes was low. CCA showed contrasting abundance patterns of frequent meadow species related to P and K availability. Holcus lanatus exhibited competitive advantage under extremely low P availability. Increase in P availability under bracken may have occurred through promoting the leaching of Fe and Al. By increasing P availability for its growth and increasing N limitation for other species, bracken can gain a competitive advantage from the soil resource-niche perspective. Its ability to increase soil P availability, along with the physiological mechanisms behind its high P acquisition efficiency, seem to differentiate bracken from other species of competitive ecological strategy, which are mainly confined to nutrient-rich environments. This enabled bracken to invade P-deficient meadows. [ABSTRACT FROM AUTHOR]

Plant–soil feedbacks (PSFs) are considered a key mechanism generating frequency‐dependent dynamics in plant communities. Negative feedbacks, in particular, are often invoked to explain coexistence and the maintenance of diversity in species‐rich communities. However, the primary modelling framework used to study PSFs considers only two plant species, and we lack clear theoretical expectations for how these complex interactions play out in communities with natural levels of diversity. Here, we extend this canonical model of PSFs to include an arbitrary number of plant species and analyse the dynamics. Surprisingly, we find that coexistence of more than two species is virtually impossible, suggesting that alternative theoretical frameworks are needed to describe feedbacks observed in diverse natural communities. Drawing on our analysis, we discuss future directions for PSF models and implications for experimental study of PSF‐mediated coexistence in the field. [ABSTRACT FROM AUTHOR]

Janzen–Connell effects (JCEs), specialised predation of seeds and seedlings near conspecific trees, are hypothesised to maintain species richness. While previous studies show JCEs can maintain high richness relative to neutral communities, recent theoretical work indicates JCEs may weakly inhibit competitive exclusion when species exhibit interspecific fitness variation. However, recent models make somewhat restrictive assumptions about the functional form of specialised predation—that JCEs occur at a fixed rate when offspring are within a fixed distance of a conspecific tree. Using a theoretical model, I show that the functional form of JCEs largely impacts their ability to maintain coexistence. If predation pressure increases additively with adult tree density and decays exponentially with distance, JCEs maintain considerably higher species richness than predicted by recent models. Loosely parameterising the model with data from a Panamanian tree community, I elucidate the conditions under which JCEs are capable of maintaining high species richness. [ABSTRACT FROM AUTHOR]

Soil microorganisms play a major role in shaping plant diversity, not only through their direct effects as pathogens, mutualists, and decomposers, but also by altering the outcome of plant interactions. In particular, previous research has shown that the soil community often generates frequency-dependent feedback loops among plants that can either stabilize or destabilize species interactions and thereby promote or hinder species coexistence. However, recent insights from modern coexistence theory have shown that microbial effects on plant coexistence depend not only on these stabilizing or destabilizing effects, but also on the degree to which they generate competitive fitness differences. While many previous experiments have generated the data necessary for evaluating microbially mediated fitness differences, these effects have rarely been quantified in the literature. Here, we present a meta-analysis of data from 50 studies, which we used to quantify the microbially mediated (de)stabilization and fitness differences derived from a classic plant-soil feedback model. We found that across 518 plant species pairs, soil microbes generated both stabilization (or destabilization) and fitness differences, but also that the microbially mediated fitness differences dominated. As a consequence, if plants are otherwise equivalent competitors, the balance of soil microbe-generated (de)stabilization and fitness differences drives species exclusion much more frequently than coexistence or priority effects. Our work shows that microbially mediated fitness differences are an important but overlooked effect of soil microbes on plant coexistence. This finding paves the way for a more complete understanding of the processes that maintain plant biodiversity. [ABSTRACT FROM AUTHOR]

Droughts affect plant communities, but their impacts may be mediated by soil biota. Soil communities may ameliorate drought stress, and droughts may leave legacies of altered soil communities that may affect future plant growth. However, it is not yet understood which groups of soil biota in particular affect plant performance under drought, nor which groups contribute to drought‐legacy effects on future plant growth. We hypothesized that increasing soil‐community complexity ameliorates drought stress and that drought‐legacy effects are species‐specific and soil‐community‐dependent. To test these hypotheses, we performed a two‐phase experiment with six grassland species. In the first phase, we examined plant performance under drought and ambient conditions, in soils inoculated with a sterilized inoculum, or increasingly complex soil communities created by wet‐sieving through 20‐, 40‐ and 200‐µm mesh sieves. In the second phase, we examined drought‐legacy effects on conspecific plant performance. We separately analysed plant performance in both phases, and integrated data from both phases using structural equation models. Drought effects on first‐phase root biomass depended on soil inoculum, and this interaction differed among plant species, while effects on shoot biomass differed among species, but did not depend on inoculum. Only one species experienced drought‐stress‐ameliorating effects of soil biota. Drought‐legacy effects on plant performance were positive, but depended on soil inoculum in case of root biomass, and on soil inoculum and species identity in case of shoot biomass. Drought‐legacy effects were often mediated by first‐phase biomass. In some species this effect was independent of inoculum, suggesting an abiotic legacy effect. In others, low first‐phase biomass corresponded with high second‐phase performance in presence of the most complex soil community. We conclude that drought‐legacy effects on plant performance were soil‐community‐dependent but positive, suggesting that plants establishing after drought may benefit from increased nutrient availability and more positive impacts of soil biota. [ABSTRACT FROM AUTHOR]

Rapid climate change imperils many small-ranged endemic species as the climate envelopes of their native ranges shift poleward. In addition to abiotic changes, biotic interactions are expected to play a critical role in plant species' responses. Below-ground interactions are of particular interest given increasing evidence of microbial effects on plant performance and the prevalence of mycorrhizal mutualisms. We used greenhouse mesocosm experiments to investigate how natural northward migration/assisted colonization of Rhododendron catawbiense, a small-ranged endemic eastern U.S. shrub, might be influenced by novel below-ground biotic interactions from soils north of its native range, particularly with ericoid mycorrhizal fungi (ERM). We compared germination, leaf size, survival, and ERM colonization rates of endemic R. catawbiense and widespread R. maximum when sown on different soil inoculum treatments: a sterilized control; a non-ERM biotic control; ERM communities from northern R. maximum populations; and ERM communities collected from the native range of R. catawbiense. Germination rates for both species when inoculated with congeners' novel soils were significantly higher than when inoculated with conspecific soils, or non-mycorrhizal controls. Mortality rates were unaffected by treatment, suggesting that the unexpected reciprocal effect of each species' increased establishment in association with heterospecific ERM could have lasting demographic effects. Our results suggest that seedling establishment of R. catawbiense in northern regions outside its native range could be facilitated by the presence of extant congeners like R. maximum and their associated soil microbiota. These findings have direct relevance to the potential for successful poleward migration or future assisted colonization efforts. [ABSTRACT FROM AUTHOR]

Interspecific interactions between plants influence plant phenotype, distribution, abundance, and community structure. Each of these can, in turn, impact sediment biogeochemistry. Although the population and community level impacts of these interactions have been extensively studied, less is known about their effect on sediment biogeochemistry. This is surprising given that many plants are categorized as foundation species that exert strong control on community structure. In southern California salt marshes, we used clipping experiments to manipulate aboveground neighbor presence to study interactions between two dominant plants, Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica). We also measured how changes in cordgrass stem density influenced sediment biogeochemistry. Pickleweed suppressed cordgrass stem density but had no effect on aboveground biomass. For every cordgrass stem lost per square meter, porewater ammonium increased 0.3–1.0 µM. Thus, aboveground competition with pickleweed weakened the effects of cordgrass on sediment biogeochemistry. Predictions about plant–soil feedbacks, especially under future climate scenarios, will be improved when plant–plant interactions are considered, particularly those containing dominant and foundation species. [ABSTRACT FROM AUTHOR]

Abstract Plant‐soil feedbacks (PSFs) have been shown to strongly affect plant performance under controlled conditions, and PSFs are thought to have far reaching consequences for plant population dynamics and the structuring of plant communities. However, thus far the relationship between PSF and plant species abundance in the field is not consistent. Here, we synthesize PSF experiments from tropical forests to semiarid grasslands, and test for a positive relationship between plant abundance in the field and PSFs estimated from controlled bioassays. We meta‐analyzed results from 22 PSF experiments and found an overall positive correlation (0.12 ≤ r¯ ≤ 0.32) between plant abundance in the field and PSFs across plant functional types (herbaceous and woody plants) but also variation by plant functional type. Thus, our analysis provides quantitative support that plant abundance has a general albeit weak positive relationship with PSFs across ecosystems. Overall, our results suggest that harmful soil biota tend to accumulate around and disproportionately impact species that are rare. However, data for the herbaceous species, which are most common in the literature, had no significant abundance‐PSFs relationship. Therefore, we conclude that further work is needed within and across biomes, succession stages and plant types, both under controlled and field conditions, while separating PSF effects from other drivers (e.g., herbivory, competition, disturbance) of plant abundance to tease apart the role of soil biota in causing patterns of plant rarity versus commonness.

Abstract Background Large-scale afforestation can significantly change the ground cover and soil physicochemical properties, especially the soil fertility maintenance and water conservation functions of artificial forests, which are very important in semi-arid mountain ecosystems. However, how different tree species affect soil nutrients and soil physicochemical properties after afforestation, and which is the best plantation species for improving soil fertility and water conservation functions remain largely unknown. Methods This study investigated the soil nutrient contents of three different plantations (Larix principis-rupprechtii, Picea crassifolia, Pinus tabuliformis), soils and plant-soil feedbacks, as well as the interactions between soil physicochemical properties. Results The results revealed that the leaves and litter layers strongly influenced soil nutrient availability through biogeochemical processes: P. tabuliformis had higher organic carbon, ratio of organic carbon to total nitrogen (C:N) and organic carbon to total phosphorus (C:P) in the leaves and litter layers than L. principis-rupprechtii or P. crassifolia, suggesting that higher C:N and C:P hindered litter decomposition. As a result, the L. principis-rupprechtii and P. crassifolia plantation forests significantly improved soil nutrients and clay components, compared with the P. tabuliformis plantation forest. Furthermore, the L. principis-rupprechtii and P. crassifolia plantation forests significantly improved the soil capacity, soil total porosity, and capillary porosity, decreased soil bulk density, and enhanced water storage capacity, compared with the P. tabuliformis plantation forest. The results of this study showed that, the strong link between plants and soil was tightly coupled to C:N and C:P, and there was a close correlation between soil particle size distribution and soil physicochemical properties. Conclusions Therefore, our results recommend planting the L. principis-rupprechtii and P. crassifolia as the preferred tree species to enhance the soil fertility and water conservation functions, especially in semi-arid regions mountain forest ecosystems.

Purpose: Rhizosphere bacterial communities ('rhizobacteria') can mediate plant-soil feedbacks that enhance plant drought tolerance, but the composition and ecological characteristics of these populations are poorly understood. We investigated the impact of drought on rhizobacteria communities and the effect of propagating drought-impacted communities on the drought tolerance of naïve plants in a two-phase experiment. Methods: We tested whether propagating rhizosphere soils from drought-stressed shrub willow (Salix purpurea), or continuously watered controls, affected the performance of a subsequent generation of droughted plants. The impacts of drought on rhizobacteria and plant fitness were evaluated using 16S rRNA gene sequencing and measures of plant growth (root mass and stem length etc.) and stress (abscisic acid, osmolality). Uninoculated reference plants were used to isolate the effects of inoculation. Results: Drought had a significant and lasting impact on the structure of rhizobacterial communities, characterized by increased populations of Actinobacteria (Acidimicrobiia, Thermoleophilia and Micrococcaceae). Foliar osmolality was significantly higher in plants receiving drought-selected communities relative to uninoculated controls, but no significant differences in plant growth were observed. Inoculation with rhizosphere soil from watered controls significantly reduced plant growth. The rhizosphere of watered control plants was dominated by Proteobacteria and Bacteroidetes. Conclusions: Our findings demonstrate that plants are affected by the legacy effects of drought on the rhizosphere microbiome. This drought legacy was propagated and persisted throughout nine weeks of plant growth, independent of prevailing water stress. Drought-impacted rhizospheres had larger populations of desiccation-tolerant (ex. Arthrobacter) and putatively endophytic taxa (ex. Rhizobium) with established plant growth promoting capabilities. [ABSTRACT FROM AUTHOR]

Negative conspecific interactions have been shown to promote diversity in plant communities, as have some heterospecific interactions such as intransitive competition and facilitation. However, it is unclear whether combinations of conspecific and other heterospecific interactions can also promote diversity in plant communities. We therefore investigated the effects of heterospecific plant interaction network architecture with and without conspecific interactions on alpha diversity, beta diversity and long‐term diversity.We simulated long‐term plant community dynamics for theoretical plant interaction scenarios with modular, ring and nested networks of positive or negative heterospecific interactions and conspecific interactions, using a spatially explicit cellular automaton model that accounted for stochastic effects. Throughout the simulations several measures of diversity were recorded.The way that heterospecific interactions affected diversity depended strongly on various characteristics of the architecture of the interaction network. Negative conspecific interactions generally promoted alpha diversity and reduced beta diversity, with a few key exceptions. Positive heterospecific ring interactions that resulted in cyclic appearance and disappearance of species groups led to the greatest long‐term diversity (a measure of the total diversity over time).This study provides new theoretical insights into how the network architecture of heterospecific plant interactions can affect the diversity of plant communities over time and provides the first evidence that heterospecific plant interactions can increase long‐term diversity more than negative conspecific interactions alone. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Differences in nutrient acquisition pathways between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi are associated with greater soil organic matter accumulation and reduced inorganic nitrogen (N) availability in EM‐dominated forests. These plant–soil feedbacks are expected to influence seedling recruitment and the maintenance of diversity.Montane forests of Central America are characterized by a mosaic of AM and EM dominance. We used a seedling transplant and soil manipulation experiment on Volcán Barú, Panama, to evaluate whether patches of oak (EM‐dominated) forest and mixed (AM‐dominated) forest affect seedling growth. We predicted that (a) plant–soil feedbacks would result in lower soil inorganic N availability in oak than in mixed forests, (b) consequently AM seedlings would grow more slowly and have lower foliar N concentrations in oak forest and (c) dependence of EM seedlings on organic N uptake via mycorrhiza would mean that inorganic N addition would increase seedling performance for AM but not EM (i.e. oak) seedlings. As soil organic matter accumulation may affect seedling performance beyond altering nutrient supply, we also tested whether organic matter removal differentially affected AM and EM seedlings.Nitrogen availability was six times lower and the soil organic layer three times deeper in oak‐dominated stands compared to mixed stands. Foliar N was lower for AM seedlings growing in oak than in mixed forest, but did not differ for oak seedlings and was increased only marginally by N addition for both AM and EM seedlings growing in both AM and EM forests. Seedling growth did not respond to N addition or organic matter removal. However, AM seedlings generally grew slower in oak forest compared with AM forest, consistent with lower foliar N concentration and low‐light availability. These results suggest that changes in soil nitrogen availability have a limited effect on seedling growth.In the neotropics, EM tree communities occur at high elevation. Future upslope migration of trees may result in AM‐dominated tree communities encountering unfavourable soil conditions generated by EM‐dominated canopies. While longer term experiments are needed, our results suggest that AM seedlings may not be able to tolerate conditions associated with EM forest. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Across the tree of life, organisms modify their local environment, rendering it more or less hospitable for other species. Despite the ubiquity of these processes, simple models that can be used to develop intuitions about the consequences of widespread habitat modification are lacking. Here, we extend the classic Levins metapopulation model to a setting where each of n species can colonize patches connected by dispersal, andwhen patches are vacated via local extinction, they retain a "memory" of the previous occupant--modeling habitat modification. While this model can exhibit a wide range of dynamics, we draw several overarching conclusions about the effects of modification and memory. In particular, we find that any number of species may potentially coexist, provided that each is at a disadvantage when colonizing patches vacated by a conspecific. This notion is made precise through a quantitative stability condition, which provides a way to unify and formalize existing conceptual models. We also show that when patch memory facilitates coexistence, it generically induces a positive relationship between diversity and robustness (tolerance of disturbance). Our simple model provides a portable, tractable framework for studying systems where species modify and react to a shared landscape. [ABSTRACT FROM AUTHOR]

We tested the 'enemy release hypothesis' in relation to Lonicera japonica to determine the effects of soil microbes on plant growth. It was hypothesized that plant performance in the introduced range in Australia would be increased by escaping natural enemies in soils in its native range of Japan, and thus there was increased likelihood of invasion success. Greenhouse experiments were carried out where plants (stem cuttings) of L. japonica were inoculated with soil microbiota (conspecifics vs. heterospecifics) from either the native range in Japan or the introduced range in Australia. Survival rates and plant growth characteristics were documented, and overall plant performance as feedbacks were calculated. The results showed that the growth of L. japonica was influenced by soil microbial communities. Plant growth performance indicated strong negative feedback when grown in its native-range soil and positive feedback when grown in its introduced range soil. Difference between ranges was noticed that includes more positive feedback when L. japonica was grown in conspecific soil compared to when it was grown in the conditioned by heterospecifics from the introduced range and more negative feedback in conspecific soils compared to heterospecific soil in the native range. The findings are consistent with the 'enemy release hypothesis' and clearly indicate that plant–soil microbes' interactions of L. japonica can play an important role in facilitating the survival and growth of L. japonica in its introduced range. [ABSTRACT FROM AUTHOR]

Abstract The enemy release hypothesis (ERH) attributes the success of some exotic plant species to reduced top‐down effects of natural enemies in the non‐native range relative to the native range. Many studies have tested this idea, but very few have considered the simultaneous effects of multiple kinds of enemies on more than one invasive species in both the native and non‐native ranges. Here, we examined the effects of two important groups of natural enemies–insect herbivores and soil biota–on the performance of Tanacetum vulgare (native to Europe but invasive in the USA) and Solidago canadensis (native to the USA but invasive in Europe) in their native and non‐native ranges, and in the presence and absence of competition. In the field, we replicated full‐factorial experiments that crossed insecticide, T. vulgare–S. canadensis competition, and biogeographic range (Europe vs. USA) treatments. In greenhouses, we replicated full‐factorial experiments that crossed soil sterilization, plant–soil feedback, and biogeographic range treatments. We evaluated the effects of experimental treatments on T. vulgare and S. canadensis biomass. The effects of natural enemies were idiosyncratic. In the non‐native range and relative to populations in the native range, T. vulgare escaped the negative effects of insect herbivores but not soil biota, depending upon the presence of S. canadensis; and S. canadensis escaped the negative effects of soil biota but not insect herbivores, regardless of competition. Thus, biogeographic escape from natural enemies depended upon the enemies, the invader, and competition. Synthesis: By explicitly testing the ERH in terms of more than one kind of enemy, more than one invader, and more than one continent, this study enhances our nuanced perspective of how natural enemies can influence the performance of invasive species in their native and non‐native ranges.