Tree Diversity Reduces Soil Carbon Temperature Sensitivity

The temperature sensitivity of soil carbon decomposition (Q₁₀) is a key determinant of terrestrial carbon–climate feedbacks under global warming. However, the mechanisms through which tree species diversity modulates Q₁₀ remain poorly understood. Using a long-term biodiversity manipulation experiment in a subtropical forest, we investigated how increasing tree species richness affects Q₁₀ by altering soil carbon stabilization processes and microbial functional composition. We found that tree species richness significantly reduced Q₁₀, reflecting enhanced soil carbon stability. This effect was mediated by increased accumulation of chemically recalcitrant compounds and a higher proportion of mineral-associated organic matter. In parallel, tree species richness induced functional shifts in microbial communities, particularly fungi, favoring saprotrophic taxa and increasing the relative abundance of microbial Y-strategists—organisms characterized by high growth efficiency and low respiratory carbon loss. These microbial functional shifts promote rapid assimilation and stabilization of soil labile carbon, contributing to slower carbon turnover and reduced Q₁₀. Together, our results demonstrate that tree species richness enhances soil carbon retention and mitigates climate feedbacks by restructuring microbial strategies and promoting long-term carbon stabilization pathways.