Eight-year snow removal affects soil organic carbon fractions in a subalpine Picea asperata forest

Climate warming is driving a reduction in snow cover in subalpine regions, which may have significant implications for forest carbon pools. We conducted an eight-year snow removal experiment in a subalpine Picea asperata forest in western Sichuan to investigate how snowpack decline affects soil carbon dynamics across seasons. Using soil organic carbon fractionation and metagenomics approaches, we analyzed changes in microbial community structure, carbon-cycle functional genes, and the content and potential stability of organic carbon components. Snow removal reshaped the microbial community structure, significantly increasing the total abundance of carbon decomposition-related genes by 7.04%, while the abundance of carbon fixation-related genes remained largely unaffected. Concurrently, snow removal exhibited distinct seasonal effects on different organic carbon fractions. During the growing season, it promoted the short-term accumulation of labile carbon fractions, with soil organic carbon (SOC), easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC) increasing by 15.82%, 7.10%, 52.82%, and 39.17%, respectively. In winter, however, it significantly reduced the SOC, EOC, MBC, mineral-associated organic carbon (MAOC), and particulate organic carbon (POC) by 33.40%, 29.05%, 48.88%, 31.04%, and 40.90%, respectively. Notably, snow removal primarily exerted an indirect influence on the content and stability potential of organic carbon by altering soil physicochemical properties in winter. Our findings highlight the critical role of winter abiotic processes in regulating soil carbon dynamics and provide important insights for predicting the response of subalpine forest soil carbon sinks to ongoing climate change.