Climate-driven soil and microbial processes regulate the microbial and plant residue carbon accumulation along an altitudinal gradient

Aims Mountain soils play a critical role in global carbon cycling, yet how altitudinal gradients regulate soil organic carbon (SOC) component formation is unclear. Methods We investigated vegetation zones along elevations in the Qilian Mountains, analyzing soil properties, microbial communities (PLFA), and SOC components. Results Results showed soil organic carbon, total nitrogen, and total microbial biomass increased with elevation. Conversely, the ratio of Gram-positive to Gram-negative bacteria (G ⁺ /G ^- ), microbial biomass per unit SOC, and the contributions of microbial necromass carbon (MNC) and plant residue carbon (PRC) to SOC declined. Structural equation modeling revealed that mean annual temperature and precipitation are primary drivers. They directly and indirectly regulate MNC and PRC formation by altering soil properties and microbial communities (e.g., fungal/bacterial ratio). This demonstrates a dominant hierarchical pathway: climate → soil properties → microbial communities → SOC components. Its explanatory power far exceeded that of microbially mediated processes alone. Conclusions These findings highlight the overarching control of macro-climate in mountain soil carbon dynamics, providing key insights for predicting soil carbon stability under climate change.