Into the functional ecology of ectomycorrhizal communities: environmental filtering of enzymatic activities

Characterizing the ecological processes driving the assembly and functional composition of ectomycorrhizal (ECM) fungal communities is an area of active research. Here, we applied a trait-based framework to address whether and how environmental filtering and niche differentiation influence the diversity of ECM fungal enzymatic activities in two oak-dominated forest ecosystems. We hypothesized that fungal enzymatic activities and ECM community assembly are influenced by the availability of targeted resources in the surrounding soil. We pinpointed a major influence of environmental filtering on ECM fungal taxonomic and functional composition. Contrasted taxonomic composition among forest ecosystems was linked to broad interspecific trait variation and entailed contrasted functional responses at community level. However, intraspecific trait variation contributed to community response within ecosystems. We characterized a strong relationship between enzymatic activities and targeted resource availability in surrounding soil, suggesting a functional role of the enzymes for the acquisition of these resources. Conversely, we did not find a significant influence of niche differentiation in ECM community assembly.Synthesis. Heterogeneous distribution of soil resources drives a community-level functional response and determines the functional and taxonomic mosaic of ECM communities in forest ecosystems.