## 4 Results and Analysis
### Spatiotemporal Variability of Carbon Sources and Sinks in the CGE  
In this study, the variation coefficient of NEP was further calculated to analyze the stability of the spatial variation of NEP. The greater the coefficient of variation is, the more frequent and volatile the NEP value is. Figure 9 shows the spatial distribution of the NEP variation coefficient in the study area. It can be seen from Figure 9 that the mean variation coefficient of NEP in the CGE was 0.027, which shows good stability. Most areas in the study area were at a \"low\" degree of variation, which means high stability, accounting for about 82.42% of the total grassland. They were mainly distributed in areas west of 400 mm isohyet, mainly in the Inner Mongolia steppe and the Qinghai-Tibet Plateau, which are less affected by human activities. The \"relatively low \" degree of variation accounted for 11.04% of grassland, mainly distributed near the 400 mm isohyet and partially distributed in the south areas. The areas with a \"medium\" degree accounted for 2% of grassland and were distributed near the 400 mm isohyet. The area with a \"relatively high\" degree of variation accounted for about 3%, and the distribution was scattered in a small range in all regions. Regions with \"high\" levels of variation accounted for about 0.2%. Correlation between the Spatiotemporal Evolution of Carbon Sources and Sinks and Climatic Factors in the CGE  
Figure 10 shows the correlation coefficient and partial correlation coefficient between NEP and climatic factors (temperature and precipitation) in the CGE. It can be seen from Figure 10 that the average correlation coefficient between the NEP and precipitation in the CGE was 0.09, and the NEP of the CGE was positively correlated with precipitation. The regions with a significant positive correlation between NEP and precipitation accounted for 1.60% of the total area of the CGE, mainly located in the Qinghai-Tibet Plateau and Inner Mongolia grassland. The NEP of the CGE in these regions increased with the increase in precipitation. The regions with a significant negative correlation between NEP and precipitation accounted for 35.27% of the total area of the CGE. In these regions, with the increase in precipitation, soil respiration carbon consumption increased and the NEP of the CGE decreased. The average correlation coefficient between NEP and temperature in the CGE was \(-\)0.06, and the NEP of the CGE was negatively correlated with temperature. The regions with a significant negative correlation between NEP and temperature accounted for 53.72% of the total area of the CGE, which were mainly located in the south of China,  
Figure 8: The proportion of variation trends of NEP in the CGE of different provinces. indicating that the increase in temperature hinders the accumulation of NEP. This may be because the increase in temperature reduces the relative humidity, and the transpiration of vegetation will remain high, resulting in the non-synchronization of water and heat required for vegetation growth, resulting in less total NPP accumulated in the grassland ecosystem. At the same time, the increase in temperature increases soil respiration and consumes a large amount of organic carbon, so the NEP of the CGE decreases. The regions with a significant positive correlation between NEP and temperature accounted for 2.25% of the total area of the CGE and were mainly distributed in the north of Qinghai, Gansu, Inner Mongolia and other regions, which further fully shows that temperature was mainly an obstacle to NEP in the study area. Under the conditions of constant temperature, the partial correlation analysis between NEP and precipitation showed that the significant positive correlation area accounted for 4.78% of the total area of the CGE. When the influence of precipitation on NEP was controlled, the proportion of areas with a significant negative correlation between NEP and temperature in the total area of the CGE decreased to 52.67%, and the area with a significant positive correlation increased slightly.