Temporal dynamics and drivers of soil organic carbon following ecological restoration on the Qinghai-Tibet Plateau

Investigating soil organic carbon (SOC) dynamic and its controlling factors is essential for improving soil carbon sequestration in ecological restoration areas. However, the temporal variations in SOC content and composition in alpine ecological restoration areas remain poorly understood. In this study, soil physicochemical properties (pH, aggregates, total and available nitrogen, total and available phosphorus, and available potassium), enzyme activity (sucrase, cellulase, alkaline protease, and alkaline phosphatase), microbial characteristics, and SOC composition were analysed to investigate the temporal changes in SOC content and its major controlling factors in alpine ecological restoration areas. Results showed that SOC content continuously increased following ecological restoration. Lignin and phenols were more abundant following ecological restoration, whereas the relative abundances of aromatic hydrocarbons, alkanes and alkenes exhibited the opposite trend, indicating a shift from microbially derived to plant-derived SOC inputs following ecological restoration. Soil enzyme activities and microbial community characteristics responded significantly to restoration, and the relative importance of stochastic processes in bacterial community assembly increased with restoration time. Partial least squares path modeling (PLS-PM) revealed that restoration time was the dominant factor associated with SOC dynamics through both direct and indirect effects mediated by soil properties, SOC composition, and microbial communities. Correlation analysis further identified soil total nitrogen (TN) as the factor most strongly associated with SOC content. These findings provide mechanistic insights into SOC accumulation following restoration and offer a scientific basis for enhancing carbon sequestration in degraded alpine ecosystem.