The alpine meadows of the Qinghai-Tibet Plateau are vital ecosystems that contribute significantly to plant productivity, multifunctionality, and carbon sequestration. However, predicting the future trajectory of these ecosystems requires a comprehensive understanding of how they respond to multiple global change drivers, particularly enhanced nitrogen (N) deposition and altered precipitation patterns. This study explores the combined effects of N deposition and altered water availability on plant productivity and associated soil dynamics in an alpine meadow on the northeastern Qinghai-Tibet Plateau. In 2017, a field experiment was established with three replicates, using a randomized block design with factorial treatments of N addition (10 g m^-2 a^-1) and precipitation manipulation (±50% of ambient rainfall). Comprehensive measurements taken in 2024 included aboveground net primary productivity (ANPP), belowground net primary productivity (BNPP, 0-40 cm depth), root turnover rate, ecosystem net primary productivity (NPP), and key soil properties (pH, soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP)). The results indicated primarily additive effects of N addition and precipitation manipulation on community ANPP, with notable variations in responses among plant functional groups. N addition alone increased ANPP by 30.0%, driven by enhanced growth of graminoids and forbs, while a 50% reduction in precipitation (CK-50%) caused a 30.0% decrease in ANPP relative to ambient conditions. Vertical stratification in soil pH was observed, with surface soil (0-10 cm) pH significantly decreasing under most treatments, except with increased precipitation (CK+50%), while deep soil (10-40 cm) pH generally increased. Despite shifts in plant productivity, SOC, TN, and TP remained statistically unchanged across all treatments, indicating stability in bulk soil nutrient pools. However, the experimental manipulations led to significant declines in root processes and overall ecosystem carbon fixation, with BNPP decreasing by an average of 26.1% and root turnover rate dropping by 21.3%. Consequently, total ecosystem NPP decreased by an average of 17.3% under these altered resource regimes. These findings suggest that N deposition and altered precipitation regimes regulate alpine meadow productivity by influencing functional group responses and plant carbon allocation strategies. Under N enrichment and/or water stress, ecosystems reduce investment in root growth and turnover, which may optimize short-term aboveground growth but significantly impair long-term carbon sequestration capacity. This study highlights the crucial role of belowground processes, particularly root production dynamics and carbon allocation, in shaping the carbon sink function of alpine meadows. Understanding root dynamics and their sensitivity to changing environmental conditions is essential for developing accurate models of ecosystem carbon cycling under ongoing global changes.