Soil phosphorus drives variation in diazotrophic communities in a subtropical nitrogen-rich forest

•The dominant genus of the diazotrophic communities changed from Cyanobacteria to Rhizobiales in subtropical N-rich and P-limited forests.•Proteobacteria taxa respond positively to microbial mechanisms triggered by P scarcity under different N treatments.•Heterotrophic diazotrophic bacteria remain active in subtropical N-rich and P-limited forests.•Soil AP drives variation in the structure of diazotrophic communities.