## 4 Discussion
### Climate-Driven Mechanisms of the Carbon Budget  
The driving factors and mechanisms of the changes in the AGQTP are still debated [23; 28; 52]. Most previous studies have concluded that climate change is the primary cause [7; 13]. However, the following question remains: whether temperature or precipitation is the dominant climatic factor and how does it drive the carbon budget? Various studies have reported different conclusions and interpretations on this matter. For instance, a study has shown that temperature changes have a greater influence on GPP than changes in precipitation and solar radiation throughout the entire QTP [53]. Another study has also concluded that climate warming is the primary driving force behind the improvement of vegetation on the QTP, similar to the vegetation growth promotion mechanism in the Pan-Arctic region [23]. However, some other studies have reported that increasing temperature exerted complex effects on the NPP and that precipitation is the primary driving force behind the changes in the AGQTP [7; 17; 54]. In contrast to GPP, the ER of the AGQTP is primarily driven by temperature, and previous studies have consistently demonstrated this [24; 55; 56]. In contrast, there is a high level of inconsistency in previous studies regarding the climate-driven mechanism of NEP. Some studies have demonstrated that the NEP of the AGQTP is primarily affected by temperature [29], while others have indicated that precipitation is the dominant factor [7]. Furthermore, a study has even suggested that the NEP of the AGQTP is negatively correlated with both precipitation and temperature, which are the factors hindering the formation of carbon sinks [31]. To clarify the driving mechanism of climatic factors (temperature and precipitation) on the carbon budget of the AGQTP, this study conducted a comprehensive and systematic analysis from multiple perspectives, including temporal differences, spatial distribution, and trend dynamics. Analysis based on annual data showed that, throughout the entire QTP, the NEP and ER were mainly driven by precipitation and temperature, respectively, while the GPP was roughly equally driven by precipitation and temperature during 2000-2020 (Figure 5a). However, the impact of climatic factors on the carbon budget exhibited significant spatiotemporal heterogeneity, which was consistent with findings from previous studies [7; 29]. Firstly, a drastic temporal variation was found in the impact of climatic driving factors on the carbon budget, where the driving factors may have changed around 2010 (Figures 5b,c and A2). Prior to 2010, the carbon budget was primarily influenced by air temperature, especially for GPP and ER. However, after 2010, it appears that precipitation may have replaced temperature and become the primary climatic driving factor of the carbon budget, while the rising temperature hindered the growth of the carbon budget, especially for the GPP and NEP. A recent study on the net primary productivity (NPP) of grasslands on the QTP also reached a similar conclusion, indicating a shift from temperature to precipitation as the controlling factor for alpine grassland productivity from 2000-2009 to 2010-2019 [57]. During 2011-2015, there was a significant decrease in the precipitation on the AGQTP, reaching the lowest level in 21 years, while the temperature exhibited an increasing trend (Figure 1b). Previous studies on the QTP have confirmed that warming will lead to an increase in ecosystem evapotranspiration, thereby exacerbating the soil water deficit [23; 58]. Most of the alpine grasslands on the QTP are distributed in semi-arid and arid climate zones (Figure 6). The contrasting trends of temperature and precipitation made these grasslands more drought-susceptible, and the inadequate water supply and relatively high temperature severely constrained the carbon sequestration capacity of the grasslands [59]. Consequently, the GPP and NEP of the AGQTP decreased drastically from 2012 to 2015 (Figure 3).