Mixed planting enhances soil multi‐nutrient cycling by homogenizing microbial communities across soil vertical scale

Abstract Soil multi‐nutrient cycling (SMC) driven by microbial communities determines the primary productivity of forests. While functional microbes and microbial community composition are thought to contribute to SMC, the importance of different microbial communities in SMC enhancement in forest ecosystems are largely unknown. Here, we aimed to decode the underlying mechanisms of bacterial and fungal communities in the surface (0–20 cm) and subsurface soils (20–40 cm) that drive SMC in two afforestation models: pure plantation (Chinese fir) and mixed plantation (different tree varieties). Mixed planting significantly enhanced the SMC along the soil vertical spatial scale, implying that mixed planting effectively alleviated soil degradation caused by pure planting. This was attributed to the homogenization effect of mixed planting on bacterial and fungal community assemblies across the soil vertical scales. Specifically, fungal communities mainly contributed to SMC in the surface soil in mixed plantations, and bacterial communities were the primary drivers of SMC in the subsurface soil. Furthermore, multiple regression and structural equation modeling confirmed that specific key fungal taxa preferentially mediate the transformation of available phosphorus and soil organic carbon, and contribute 77.0% of SMC variation in the surface soil, while bacterial taxa mainly drive the transformation of ammonium nitrogen and soil organic carbon, and account for 60.0% of SMC variation in the subsurface soil. This study highlights the different patterns of bacterial and fungal community assembly, and their function in SMC along the soil vertical spatial scale, and advances the understanding of the roles of soil microbial communities in degraded forest soil remediation.