Data and code: Root causes of belowground processes: Tree mycorrhizal associations outweigh tree richness

This repository contains the R code and data used to analyze the relationships among tree diversity, mycorrhizal associations, soil microbial communities, and ecosystem functions in this study. Using a long‑term tree diversity experiment at the Smithsonian Environmental Research Center, we tested how tree species richness and tree mycorrhizal association (arbuscular vs. ectomycorrhizal) shape soil microbial diversity and composition. Ectomycorrhizal (EM) fungal diversity and turnover were strongly driven by tree mycorrhizal association, while arbuscular mycorrhizal (AM) fungal abundance responded to mycorrhizal association and AM biomass increased with tree richness. Soil ecosystem functions were not directly affected by tree richness or mycorrhizal type, but instead by shifts in fungal diversity and community composition, which correlated with nutrient pools and soil organic carbon. These results demonstrate that tree mycorrhizal association influences both EM and AM fungal communities and indirectly shapes ecosystem processes via belowground microbiomes.