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

Soil microbial communities are fundamental to ecosystem multifunctionality (EMF), yet their responses to environmental changes in karst regions remain poorly understood. Here, we investigated soil microbial attributes—diversity, keystone taxa abundance, 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 abundance, and soil EMF increased along the elevation gradient. Compared to microbial diversity, microbial network complexity and keystone taxa abundance exhibited stronger positive effects on soil EMF. Notably, the positive effects of network complexity and keystone taxa abundance on soil EMF decreased with increasing threshold levels of EMF, yet keystone taxa abundance 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 keystone taxa abundance and microbial network complexity in maintaining soil EMF under environmental change, providing a framework for predicting and managing ecosystem function in karst mountain ecosystems.