Increasing tree phylogenetic diversity stimulates microbial functional potential in a subtropical forest

Soil microbial functions are closely related to ecosystem productivity, carbon sequestration, and their responses to global change. Tree diversity has been found to impact microbial community composition, diversity, and functions, but how it modulates the linkage between microbial community facets and functions remains unclear. Here, 45 plots covering a natural gradient of tree phylogenetic diversity (TPD) were selected in a subtropical forest of southwest China to explore how increasing TPD impacts soil microbial community facets and microbial functional potential, with the latter being assessed by the abundances of carbon, nitrogen, and phosphorus cycling-related functional genes. Our results indicate that soil fungal alpha diversity increased significantly, but bacterial alpha diversity did not change as TPD increased. Both soil microbial network complexity and stability improved significantly with increasing TPD. Ultimately, increasing TPD promoted soil microbial functional potential by stimulating soil carbon and nitrogen availability, microbial keystone diversity, and network stability collectively. These findings emphasize the critical roles of keystone taxa and network stability as microbial factors in stimulating soil microbial function in response to increasing TPD, and provide useful information for predicting ecosystem functions in Earth system models.