Interspecific plant-plant interactions increase the soil microbial network stability, shift keystone microbial taxa, and enhance their functions in mixed stands

Mixed forests can improve biomass productivity and soil quality compared with monospecific stands. Soil microbial communities are important for the functions and services in forests. However, the mechanisms by which mixed stands improve tree growth and soil nutrient availability remain unclear. Here, we assessed the soil microbial communities and soil characteristics of Betula albosinensis and Picea asperata growing alone (B and P), monospecific stands of B. albosinensis (BB) and P. asperata (PP), and a mixed stand of B. albosinensis with P. asperata (BP). Results showed that soil characteristics, composition and network of bacterial and fungal community differed significantly between tree species and stand types. Compared with monospecific stands, the mixed stand had 1) 65.36%, 57.51%, and 17.42% higher in SOC, TN, and SAP concentration, respectively; 2) higher diversity of soil bacterial and fungal communities; 3) better microbial networks and higher abundance of keystone bacterial and fungal taxa associated with nutrient decomposition and utilization. The results indicated that increasing of soil bacterial and fungal diversity, network stability and specialized keystone bacterial and fungal taxa by interspecific plant-plant interactions in mixed forests improve soil nutrient availability. This study highlights the importance of sustaining soil microbial taxa and ecological function in the soil nutrient cycling processes for better forest management.