To elucidate the initial effects of nitrogen deposition on soil organic carbon （SOC） and its stability in alpine meadows， we conducted a field nitrogen addition experiment in the eastern Qilian Mountains. Aboveground biomass， soil physicochemical properties， enzyme activities， and SOC fractions were measured， and their key drivers were identified using variance partitioning. Nitrogen addition significantly increased aboveground biomass but reduced cellulase and β-glucosidase activities （P<0.05）. Particulate organic carbon （POC） content and proportion decreased markedly， whereas easily oxidizable organic carbon （EOC） and mineral-associated organic carbon （MAOC） increased significantly （P<0.05）. POC dynamics were mainly regulated by total phosphorus and carbon-acquiring enzymes， MAOC was closely associated with aboveground biomass， pH， and β-glucosidase， while EOC was primarily driven by available phosphorus and cellulase. Overall， microbial biomass carbon （17%） and dissolved organic carbon （14.1%） primarily explained short-term SOC variations. In summary， nitrogen addition enhanced soil carbon pool stability by promoting plant carbon inputs， modulating enzyme activities， and reshaping the distribution of SOC fractions. These findings reveal the pathways through which nitrogen deposition stabilizes SOC in alpine meadows， providing critical insights into carbon cycling processes and the carbon sequestration potential of fragile ecosystems under nitrogen enrichment.

Alpine meadow  /  Nitrogen addition  /  Activated carbon components  /  Carbon pool stability  /  Variance decomposition