Microbial keystone taxa and network complexity, rather than diversity, sustain soil multifunctionality along an elevational gradient in a subtropical karst mountain

Karst mountain ecosystems are among the most climate-sensitive landscapes globally, yet the relationship between subsurface microbial communities and ecosystem multifunctionality (EMF) in these fragile environments remains poorly understood. Here, we investigated soil microbial attributes—diversity, keystone taxa, and network complexity—along an elevational gradient in a karst mountain ecosystem to identify key drivers of soil EMF. Our results revealed that elevation significantly influenced microbial community composition and soil EMF. Specifically, microbial diversity decreased with increasing elevation, whereas microbial network complexity, keystone taxa, and soil EMF increased along the elevation gradient. Compared to microbial diversity, microbial network complexity and keystone taxa exhibited stronger positive effects on soil EMF. Notably, the positive effects of network complexity and keystone taxa on soil EMF decreased with increasing threshold levels of EMF, yet keystone taxa retained a significant positive effect even at the highest threshold (75%). Moreover, annual mean temperature and soil pH significantly influenced microbial characteristics, which in turn affected soil EMF. These findings highlight the pivotal roles of microbial keystone taxa and network complexity in maintaining soil EMF under environmental change, especially in high-stress conditions. These findings provide not only a framework for predicting ecosystem function in karst mountain ecosystems but also valuable insights for the management and conservation of other fragile ecosystems worldwide.