Functional traits of fine roots are primary determinants of richness and composition of microbial communities in subtropical forest soil

Aims Although plant–microbial interactions are essential in sustaining terrestrial ecosystem functions, root–microbial interactions remain poorly understood. Therefore, effects of fine root species richness, composition and biomass, and functional traits on soil microbial community richness and composition were assessed in subtropical secondary forests. Methods Fine root identity (DNA meta bar coding) was linked with microbial species (high-throughput Illumina sequencing) to reveal root effects on richness and composition of bacterial and fungal communities. Results The results showed that bacterial and fungal richness was principally determined by functional dispersion of specific root length (FDis_SRL) and community weighted means of root diameter (CWM_diam), and their richness increased with these two root parameters. Microbial community composition was mainly regulated by FDis_SRL, and the abundance of eutrophic bacteria (r-strategists, e.g., Proteobacteria and Actinobacteria ), saprotrophs and pathogens increased with FDis_SRL. These two root parameters still directly affect microbial community richness and composition even after accounting for soil and aboveground plant properties and also indirectly by increasing pH, total nitrogen, TP, and AP and decreasing C:N ratio. Furthermore, the richness and composition of fungi were more affected by fine root traits than bacteria, whereas bacteria were more strongly influenced by soil properties. Conclusions Overall, soil microbial community richness and composition in subtropical secondary forests were primarily determined by fine root functional traits, especially FDis_SRL and CWM_diam. These results will improve our understanding of the important role of root–microbial interactions in terrestrial biogeochemical processes.