Identifying the ecological processes that structure communities and the consequences for ecosystem function is a central goal of ecology. The recognition that fungi, bacteria, and viruses control key ecosystem functions has made microbial communities a major focus of this field. Because many ecological processes are apparent only at particular spatial or temporal scales, a complete understanding of the linkages between microbial community, environment, and function requires analysis across a wide range of scales. Here, we map the biological and functional geography of soil fungi from local to continental scales and show that the principal ecological processes controlling community structure and function operate at different scales. Similar to plants or animals, most soil fungi are endemic to particular bioregions, suggesting that factors operating at large spatial scales, like dispersal limitation or climate, are the first-order determinants of fungal community structure in nature. By contrast, soil extracellular enzyme activity is highly convergent across bioregions and widely differing fungal communities. Instead, soil enzyme activity is correlated with local soil environment and distribution of fungal traits within the community. The lack of structure-function relationships for soil fungal communities at continental scales indicates a high degree of functional redundancy among fungal communities in global biogeochemical cycles.T he structure and function of ecological communities are intimately linked, such that the number and identity of species within a community often affect the key ecosystem properties of primary productivity (1), resistance and resilience to disturbance (2), and rates of nutrient cycling (3). However, understanding the extent to which structure-function relationships hold across communities and over large spatial scales continues to be a major goal of ecological research. Identifying these relationships for microbial organisms is particularly critical, because these organisms control rates of key ecosystem processes (the cycling of nitrogen, phosphorus, and carbon) (4) and directly affect the community structure of plants and animals through pathogenic or mutualistic interactions (5). As such, microbial activity is also intrinsic to Earth system models that inform citizens and policy makers of ecosystem dynamics and energy exchange between the biosphere and the atmosphere (6). As in plant communities of tropical rainforests (7), the incredible number of microbial taxa on Earth has been a challenge for understanding the link between diversity and function. Advances in DNA sequencing technology have recently allowed for a robust characterization of bacterial biogeographic patterns (8); however, to date, studies have examined structure-function relationships at a fixed scale (9-12). As a result, it is not yet clear how microbial function is linked to largescale biogeographic patterns, whether or not this link is a more reliable determinant of microbial function in global biogeochemical cycl...
Influences of soil environment and willow host species on ectomycorrhizal fungi communities was studied across an hydrologic gradient in temperate North America. Soil moisture, organic matter and pH strongly predicted changes in fungal community composition. In contrast, increased fungal richness strongly correlated with higher plant-available phosphorus. The 93 willow trees sampled for ectomycorrhizal fungi included seven willow species. Host identity did not influence fungal richness or community composition, nor was there strong evidence of willow host preference for fungal species. Network analysis suggests that these mutualist interaction networks are not significantly nested or modular. Across a strong environmental gradient, fungal abiotic niche determined the fungal species available to associate with host plants within a habitat.
Predicting the outcome of interspecific interactions is a central goal in ecology. The diverse soil microbes that interact with plants are shaped by different aspects of plant identity, such as phylogenetic history and functional group. Species interactions may also be strongly shaped by abiotic environment, but there is mixed evidence on the relative importance of environment, plant identity and their interactions in shaping soil microbial communities. Using a multifactor, split-plot field experiment, we tested how hydrologic context, and three facets of Salicaceae plant identity-habitat specialization, phylogenetic distance and species identity-influence soil microbial community structure. Analysis of microbial community sequencing data with generalized dissimilarity models showed that abiotic environment explained up to 25% of variation in community composition of soil bacteria, fungi and archaea, while Salicaceae identity influenced <1% of the variation in community composition of soil microbial taxa. Multivariate linear models indicated that the influence of Salicaceae identity was small, but did contribute to differentiation of soil microbes within treatments. Moreover, results from a microbial niche breadth analysis show that soil microbes in wetlands have more specialized host associations than soil microbes in drier environments-showing that abiotic environment changed how plant identity correlated with soil microbial communities. This study demonstrates the predominance of major abiotic factors in shaping soil microbial community structure; the significance of abiotic context to biotic influence on soil microbes; and the utility of field experiments to disentangling the abiotic and biotic factors that are thought to be most essential for soil microbial communities.
Intraspecific variation can be an important driver of ecological interactions in species‐rich communities. Predicting the effects of intraspecific variation in different environments, however, remains a major challenge. This is because we often do not quantify both the effects of functional traits on associated communities and the extent to which trait variation is due to genetics (genotype effects) vs. plasticity (environment effects). As a consequence, the relative importance of trait plasticity vs. genetic variation in structuring associated communities remains unclear. We sought to fill this gap by conducting common garden experiments with the plant Salix hookeriana across biotic (ant–aphid interactions) and abiotic (wind exposure) environmental gradients in a coastal dune ecosystem. In each experiment, we simultaneously measured plant traits and species richness of associated above‐ and below‐ground communities. We then used statistical models to quantify the relative importance of trait plasticity vs. genetic variation in structuring communities. Our major finding was that trait plasticity was more important than genetic variation in determining the number of species in associated communities. This result was consistent across different environmental contexts (experimental manipulations of ant–aphid interactions and wind exposure), multiple years, and for above‐ground arthropods and root microbes. This occurred because the traits that had the largest effect on species richness were also the most plastic. Synthesis. These results indicate that trait plasticity can be a dominant driver of above‐ and below‐ground biodiversity.
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