Functional convergence of soil fungal communities with biotic homogenization in a biodiversity hotspot

Aims Soil fungal communities playcritical roles in ecosystem functions. However, soil fungal communities are becoming homogenization under human disturbance although the functional consequences remain poorly understood. Methods Here we investigated soil fungal community composition, diversity, and functional guild structure acrossagroecosystems, grasslands, and forests in four isolated valleys of the Mountains of Southwest China, a globally recognized biodiversity hotspot. We characterized the patterns of biotic homogenization and the relative abundance of functional guilds. Community assembly processes were inferred using the iCAMP framework. Results Agroecosystems harbored 30.3% higher phylotype richness than grasslands but exhibited significantly lower β-diversity (3.25% and 4.71% lower than grasslands and forests, respectively) and higher biotic homogenization degrees. Agroecosystems hosted more abundant plant pathogens than forests and grasslands (by 361.5% and 354.0%, respectively) and more saprotrophs (by 91.3% and 72.8%), but substantially fewer ectomycorrhizal fungi (93.3% lower than forests). Soil fungal communities in agroecosystems showed the highest importance of homogeneous selection, whereas heterogeneous selection was lowest, consistent with the homogenization pattern. The richness and abundance of plant pathogens and saprotrophs increased whereas those of ectomycorrhizal fungi decreased with biotic homogenization. Bin-level assembly analysis revealed that the assembly processes were associated with functional guilds. Soil total phosphorus, nitrate, and C:P ratio were key environmental drivers of homogenization and functional guild shifts. Conclusions These findings demonstrate that agricultural activities drive fungal community convergence through environmental filtering, with cascading effects on functional guilds that may compromise ecosystem multifunctionality and long-term soil health.