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

•Soil nutrient and microbial properties varied with tree species and stand types.•Mixed forests (MF) had higher soil nutrient concentration and microbial diversity.•MF had more stable soil microbial networks than monospecific forests.•MF increased the abundance of nutrient cycling-related keystone microbial taxa.•Shifts of keystone microbial taxa in MF contribute to high nutrient availabilities.