Root traits and soil nutrient and carbon availability drive soil microbial diversity and composition in a northern temperate forest

Aims: Root traits play an important role in regulating soil microbial communities by altering soil parameters. However, how the variation of root traits across tree species affects soil microbiome under different nutrient environments is unclear. Methods: We chose six dominant ectomycorrhizal (ECM) tree species differing in root diameter in a temperate forest, and measured root growth, morphological and chemical traits, soil parameters and microbial communities under three nutrient addition treatments, including unfertilized control (CK), inorganic fertilizer (IF) and organic fertilizer (OF), using ingrowth bags. Results: Compared with CK, IF and OF additions decreased soil bacterial α-diversity, and IF addition also decreased soil fungal α-diversity. The community co-occurrence network was more complex after OF addition than CK and IF treatments. The root morphological traits (root diameter and specific root length) were positively correlated with fungal community composition, whereas root chemical traits (total soluble sugar and phenol contents) influenced the composition and α-diversity of bacterial and fungal communities in the CK and IF treatments. The root growth traits (root length and biomass) affected the composition and α-diversity of bacterial and fungal communities in all treatments. Fine root traits and soil parameters interactively explained more variation in the bacterial than the fungal communities. Conclusions: Our findings suggest that the variation of root traits across tree species, nutrient and carbon availability, and their interactions can drive soil bacterial and fungal diversity and composition.