## 5 Conclusions  
Our findings reflect the spatiotemporal variations in carbon sources/sinks in the TRSR. The alpine grassland ecosystem has carbon sequestration potential, with an average NEP of 3.74 Tg C/yr, and the carbon sink area accounts for approximately 99.15% of the total grassland area. In its spatial pattern, the NEP of the alpine grassland showed a decreasing trend from east to west. From 1985 to 2018, the NEP trend increased significantly, with an average annual growth rate of 0.40 g C/m\({}^{2}\)/yr. There were significant differences in carbon uptake capacity between the alpine meadow and alpine steppe. The alpine meadow contributed the most to the regional carbon sink, with an annual average of 2.43 Tg C/yr, whereas the alpine steppe contributed only 0.22 Tg C/yr. The correlation between precipitation and NEP was the strongest in the TRSR, and the grassland ecosystem with a statistically significantly positively correlated NEP with precipitation was approximately 15.03\(\times\)10\({}^{6}\) km\({}^{2}\), accounting for probably 45.35% of the total grassland area. In addition, temperature and NEP were also positively correlated, with a significant positive correlation area of 36.59%. Temperature and precipitation contributed synergistically to the NEP growth trends, and solar radiation had an offsetting effect on the increasing NEP trend in the TRSR. In most regions, the contribution of temperature to increasing NEP trends was greater than that of precipitation; nevertheless, precipitation was the main positive contributor to the NEP trend in the HRSP. The study of the spatio-temporal variability of carbon sequestration in the TRSR helps us understand the biogeochemical cycles of alpine ecosystems and their response to climate change, which are vital for implementing science-based classification and zoning conservation measures in the TRSNP. Figure 13: The contributions of other factors to the GPP (**a**) and NEP (**b**) trends in the TRSR. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs14194795/s1](https://www.mdpi.com/article/10.3390/rs14194795/s1)]([https://www.mdpi.com/article/10.3390/rs14194795/s1](https://www.mdpi.com/article/10.3390/rs14194795/s1)), Figure S1: Interannual variations in mean annual temperature, precipitation, and solar radiation in the grassland ecosystem of the TRSR from 1985 to 2018; Table S1: Average periods and their variance contributions to carbon fluxes. **Author Contributions:** Conceptualization, F.L. and X.Y. ; methodology, F.L. ; software, F.L. ; validation, F.L. and X.Y. ; formal analysis, F.L. ; writing--original draft preparation, F.L. ; writing--review and editing, F.L. ; visualization, F.L. ; supervision, X.Y. ; funding acquisition, X.Y. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported by the State Key Laboratory of Earth Surface Processes and Resource Ecology (2022-GS-01), the National Key Research and Development Program of China (2019 YFA0606904 & 2018 YFC509003). **Data Availability Statement:** The China meteorological forcing dataset from the website: [[http://data.tpdc.ac.cn](http://data.tpdc.ac.cn)]([http://data.tpdc.ac.cn](http://data.tpdc.ac.cn)), accessed on 10 December 2021. Carbon fluxes stimulated by BEPS is available at [[http://www.nesdc.org.cn](http://www.nesdc.org.cn)]([http://www.nesdc.org.cn](http://www.nesdc.org.cn)), accessed on 6 January 2022. The GLASS-GPP products used for validation is available at [[https://pan.baidu.com/s/ITS4g6_mnW_Qf6Y2w3](https://pan.baidu.com/s/ITS4g6_mnW_Qf6Y2w3) Mbig]([https://pan.baidu.com/s/ITS4g6_mnW_Qf6Y2w3](https://pan.baidu.com/s/ITS4g6_mnW_Qf6Y2w3) Mbig), accessed on 5 September 2022. The LAI dataset can be downloaded at [[https://www.resdc.cn/data.aspx?DATAID=336](https://www.resdc.cn/data.aspx?DATAID=336)]([https://www.resdc.cn/data.aspx?DATAID=336](https://www.resdc.cn/data.aspx?DATAID=336)), accessed on 6 January 2022.