Plant species diversity enhancing soil N cycling

Plant species diversity (PSD) regulates ecosystem functions and has been shown to promote soil nitrogen (N) availability. Nevertheless, the mechanisms underlying the effect of PSD on soil N availability have not been well explored. Here, 45 plots with a natural PSD gradient ranging from 0.15 to 3.57 were selected in a subtropical forest to explore the effect of PSD on soil N transformations. Higher PSD significantly enhanced the rates of gross N mineralization, gross nitrification, microbial N immobilization, net N mineralization, net nitrification, and the contents of soil total N and inorganic N. Structural equation modeling showed that PSD indirectly impacted gross N transformations via its roles in regulating soil organic matter, mineral and microbial traits. Higher PSD stimulated gross N mineralization and nitrification rates mainly via its positive effects on microbial biomass content and gene abundances of chiA, archaeal or bacterial amoA, while increased microbial N immobilization mainly due to its stimulation of soil organic matter. Our findings highlight the crucial role of PSD in stimulating soil N availability and provide a mechanistic understanding which can be integrated into Earth system models to better predict soil N availability and C sequestration in response to PSD.