Abstract: Alpine meadow on the Qinghai-Tibetan Plateau is an important carbon sink. Understanding how the responses of its carbon exchange to global change drivers is essential for accurately assessing the regional carbon budget. In 2017, we conducted a field manipulation experiment at the National Field Research Station for Haibei Alpine Grassland Ecosystem in Qinghai Province, established in 2017. The experiment used a randomized complete block design with a full factorial of nitrogen addition (10 g·m^-2·a^-1) and precipitation manipulation (±50% of ambient rainfall). To quantify the main and interactive effects of nitrogen deposition and altered precipitation patterns on ecosystem carbon fluxes, we measured monthly soil respiration, ecosystem respiration, gross primary productivity (GPP), and net ecosystem productivity (NEP) using static chambers coupled with an infrared gas analyzer during the growing season of 2025. Key abiotic factors (soil temperature and moisture) and vegetation productivity (above- and below-ground biomass and net primary productivity) were also monitored. The results showed that nitrogen addition significantly increased aboveground net primary productivity by 37.8%, whereas the decreased precipitation treatment reduced it by 19.0%. There was no significant interaction between nitrogen addition and precipitation manipulation. In contrast, belowground biomass, belowground net primary productivity, and ecosystem net primary productivity in the 0-40 cm soil layer did not differ among treatments. Relative to that under CK, soil respiration generally showed a declining trend across all other treatments. In contrast, ecosystem respiration, GPP, and NEP tended to increase, except under the decreased precipitation treatment. Nitrogen addition significantly increased GPP and NEP by 33.5% and 43.2%, respectively. Although precipitation manipulation had no significant main effect, its interaction with nitrogen addition was marginally significant for GPP. Structural equation modeling and correlation analyses of response ratio jointly revealed that nitrogen addition and precipitation manipulation influenced carbon flux primarily through change in soil temperature, rather than through vegetation productivity. The total effects (standardized path coefficient β>0.56) of nitrogen addition on ecosystem respiration, GPP, and NEP were stronger than those of precipitation manipulation (β=0.30). This study would provide scientific evidence for adaptive management of the carbon sink function in alpine meadows under global change scenarios.

Key words: alpine meadow, soil respiration, ecosystem respiration, gross primary productivity, net ecosystem productivity