## 5 Discussion  
Guided by the goal of a carbon peak and carbon neutralization in China, this study estimated the fine grid scale NEP of the CGE from 2010 to 2020 by coupling the VPM and SRM. The results showed that the cumulative carbon sequestration of the CGE from 2010 to 2020 was 14.46 PgC. This study identified the carbon source area and carbon sink area; the total carbon sequestration in the carbon source area was 12.75 PgC, and the total carbon emission in the carbon sink area was 0.12 PgC. In short, the carbon sink capacity of the CGE shows the spatial differentiation characteristics of being high in the northwest of China and low in the southeast of China, and this distribution characteristic strongly corresponds with the 400 mm isohyet and 0 \({}^{\circ}\)C isotherm of China, which indicates that there is a strong correlation between GE distribution and precipitation and temperature. This study further analyzed the general trend of the interannual variation of NEP in the CGE from 2010 to 2020. It was found that it has an obvious synergistic relationship with the change characteristics of precipitation in China, which may show that the decline of precipitation led to the reduction in the distribution area of the CGE and the weakening of soil respiration, which led to the decrease in NEP.  
In order to explore the response relationship between NEP and temperature and precipitation in the CGE, the correlation coefficient and partial correlation coefficient of the NEP and temperature and precipitation in the CGE were further analyzed. The results showed that the NEP of the CGE was positively correlated with precipitation (average correlation coefficient 0.09) and negatively correlated with temperature (correlation coefficient \(-\)0.06). When a certain factor was controlled unchanged, the partial correlation coefficient showed that climate factors are mainly coupled to the CGE, and precipitation and temperature jointly regulate the change and accumulation of NEP in the CGE. In addition, the study also found that the impact of temperature on NEP was significantly higher than that of precipitation in the study area.  
In short, based on the fine grid data, this study realized the estimation of carbon sources and sinks of the CGE from 2010 to 2020 and quantitatively discussed the driving relationship between the spatiotemporal change of carbon source and sink of the CGE and temperature and precipitation. This study is of great significance for China in achieving the double carbon goal. However, there are still some deficiencies. The NEP reveals the characteristics and laws of the spatial distribution of carbon sources and carbon sinks in the CGE, but the ecosystem carbon cycle and soil respiration are complex ecological processes, and there are certain uncertainties in the estimation of models. When estimating NEP, all indicators were calculated on the scale of \"year\" in this study, which erased the influence of seasonal variation on NEP to a certain extent. This study only discussed the impact of temperature and precipitation on the NEP. In addition to temperature and precipitation, the impact of human activities, topographic factors, surface evapotranspiration and other factors on the spatial distribution of NEP was not considered. Therefore, further research should widely collect actual monitoring data to estimate more accurately the ecosystem's carbon sources and sinks and consider the seasonal variation factors, as well as the fluctuation impact of human activities, meteorological factors and topographic factors on the CGE, so as to have a deeper understanding of the contribution mechanism of increasing the sinks and reducing the sources of carbon cycles in the CGE.