The interactions between plant diversity and the soil microbial community are crucial for maintaining multiple ecosystem functions. However, the underlying mechanisms of how plant diversity impacts the soil microbial biomass and community composition are still unclear. In this study, we used a biodiversity-ecosystem function experiment to explore whether tree species richness affects the soil microbial biomass and community composition through functional trait variation and community-weighted trait means (CWM). The diversity gradient covered 1, 4, 8, 16 and 32 tree species. Phospholipid fatty acid analysis was used to determine the soil's total microbial biomass and composition. We found that an increase in tree species richness decreased the soil's total microbial biomass, with a more pronounced decrease in young forests with a lower functional trait variation in root nitrogen or with resource-conservative traits (i.e., higher CWM of leaf dry matter content). An increase in tree species richness decreased the biomass ratio of gram-positive to gram-negative bacteria but did not significantly affect the fungi to bacteria ratio. The fungi to bacteria ratio significantly decreased with the CWM of leaf nitrogen content and the functional trait variation in leaf dry matter content. Both the functional trait variation and CWM of the plant leaf and root traits related to resource acquisition influenced the strength and direction of the tree species richness effect on the soil microbial community. Our findings indicated that the functional trait variation and CWM of plant functional traits of the tree communities drive the changes in soil microbial biomass and community composition, which in the long-term feedback on ecosystem functions and services they provide.

植物多样性与土壤微生物群落之间的相互作用对于维持多种生态系统功能至关重要。然而，植物多样性如何影响土壤微生物量和群落组成的潜在机制仍不清楚。在本研究中，我们使用生物多样性-生态系统功能实验来探索树种丰富度是否通过功能性状变异和群落加权性状均值（CWM）影响土壤微生物量和群落组成。多样性梯度涵盖了 1、4、8、16 和 32 个树种。磷脂脂肪酸分析用于确定土壤的总微生物生物量和组成。我们发现树种丰富度的增加降低了土壤的总微生物量，根氮功能性状变异较低或资源保守性状（即叶干物质含量较高的 CWM）的年轻森林的减少更为显着。树种丰富度的增加降低了革兰氏阳性菌与革兰氏阴性菌的生物量比，但对真菌与细菌的比例没有显着影响。随着叶片氮含量的CWM和叶片干物质含量的功能性状变化，菌菌比显着降低。与资源获取相关的植物叶根性状的功能性状变异和CWM都影响了树种丰富度对土壤微生物群落的影响强度和方向。