Plant functional trait and plant–microbe network β-diversity dominate spatial turnover of ecosystem multifunctionality in subtropical forests

Intensified human activities and climate change are accelerating biodiversity loss and the degradation of ecosystem functions. While the positive role of local (α-scale) biodiversity in sustaining ecosystem multifunctionality is well established, its drivers at broader spatial (β) scales—particularly in forest ecosystems—remain poorly understood. This study aims to clarify how biotic and abiotic factors work together to drive ecosystem multifunctionality in subtropical forests at the β scale. We integrated the survey results of plant communities, soil microbial communities, and physicochemical conditions from 24 forest plots. Ecosystem β multifunctionality (β-EMF) was quantified using Hill-Chao numbers. Multiple Regression on Distance Matrices (MRM) and distance-based structural equation model (dbSEM) were employed to assess how environmental heterogeneity and biological β-diversity shape β-EMF. The results show that both plant β-diversity (especially functional trait β-diversity) and plant–microbe network β-diversity can directly and significantly affect β-EMF. Microbial β-diversity does not directly affect β-EMF but indirectly influences β-EMF through plant β-diversity and plant–microbe network β-diversity. For abiotic factors, environmental distance (soil pH) mainly exerts a cascade effect through plant β-diversity, thereby indirectly regulating β-EMF. These findings highlight that ecosystem multifunctionality at the β-scale is governed by the interplay of abiotic gradients and biodiversity reorganization. Our research offers new insights into the relationship between biodiversity and ecosystem multifunctionality in forest ecosystems at larger scales, along with a mechanistic basis for designing multi-functional forest landscapes.