## 5 Conclusions  
This study systematically analyzed the dynamics of the carbon budget in the AG\({}_{\rm QTP}\) and its climate-driven mechanism during 2000-2020. Results indicated that the alpine grassland over the plateau acted as a carbon sink (with a mean annual NEP of 15.25 Tg C yr\({}^{-1}\)), and the annual GPP, ER, and NEP increased at rates of 0.002 Pg C yr\({}^{-2}\), 0.013 Pg C yr\({}^{-2}\), and 0.0007 Pg C yr\({}^{-2}\), respectively, during the study period. However, the rate of increase in carbon uptake and sequestration slowed down over the study period. It was found that the impact of precipitation on the carbon budget was strengthened, while the influence of temperature was weakened, during 2000-2020, and the warming rate on the QTP was greater than the wetting rate, potentially becoming a main contributing factor to the slowdown of the increase in grassland carbon sinks. In the entire period, GPP was influencedby both precipitation and temperature, while NEP and ER were primarily impacted by precipitation and temperature, respectively. However, the primary climatic driver of the carbon budget may have changed from temperature to precipitation around 2010. Our study also revealed that the positive effect of warming on the grassland's carbon uptake was strongly constrained by local water conditions on the plateau. Specifically, temperature promoted carbon fixation by the grassland only in the areas with relatively abundant water. The findings of this study also suggested that climate change, particularly variations in precipitation, had notable legacy effects on the carbon budget of the \(\mathrm{AG_{QTP}}\), and the response of belowground meristems to climate factors is likely the main cause of the legacy effect. However, additional research should be conducted to further clarify the mechanism of this legacy effect.  
**Author Contributions:** Supervision, X.Z. and B.N; conceptualization, X.Z. and B.N.; methodology, Z.H.; writing--original draft preparation, Z.H.; writing--review and editing, B.N.; investigation, Z.H., Y.Z. and M.X.; data curation, Z.H.; formal analysis, Z.H.; validation, X.Z. and B.N.; software, Z.H. and J.T.; resources, Z.H.; visualization, Z.H.; project administration, X.Z.; funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was jointly supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (grant number 2019 QZKK1002), the Major Science & Technology Special Projects of Tibet Autonomous Region (grant number XZ202101 ZD0007G), and the Tibet Autonomous Region Science and Technology Planning Project (grant number XZ202201 ZY0016G).  
**Data Availability Statement:** All data are available from the corresponding author upon rational request.  
**Conflicts of Interest:** The authors declare no conflict of interest.
Figure 17: The changes in correlation coefficients between carbon budget indicators (GPP (gressor primary productivity), ER (ecosystem respiration), and NEP (net ecosystem respiration)) and climatic factors (PPT (precipitation) and TEMP (temperature)) over sliding windows (the window length was set to 6 years after testing).