## 3 Results
### Impacts of Environment Factors on GPP Dynamics  
We presented the interannual trends of climate factors, and partial correlation analysis was conducted to evaluate the relationships between climate factors (i.e., solar radiation, precipitation, and temperature) and GPP within Northern China's ecological restoration areas (Figure 6). From Figure 6a, it can be observed that radiation is significantly increasing in the western Mongolian Plateau and the northern Loess Plateau. A positive correlation between solar radiation and GPP was observed in 78.2% of the study areas, particularly in the Loess Plateau, western Inner Mongolian Plateau, and northern Xinjiang, indicating that solar radiation positively influences GPP. The Loess Plateau, in particular, exhibited a significant positive correlation, covering 18.3% of the study area, underscoring the role of solar radiation in enhancing vegetation growth. Conversely, negative correlations were found in 21.8% of the study area including regions such as the Northeast Plain, eastern Inner Mongolian Plateau, Tianshan Mountains, and parts of the Junggar Basin, suggesting that solar radiation may inhibit vegetation growth in these areas (Figure 6b).  
In areas with ecological restoration projects, the increasing trend of precipitation over the past 20 years showed a pattern of higher values in the west and lower values in the east, with an overall upward trend, although there was a decline observed in the Tianshan Mountains and the Tarim Basin (Figure 6c). A total of 92.0% of the vegetation exhibited a positive correlation between precipitation and GPP, especially in the Northeastern Plain, the Loess Plateau, the Inner Mongolian Plateau, and the northwestern part of Xinjiang, indicating that precipitation has a beneficial effect on GPP. Significant positive correlations were particularly evident in the Northeastern Plains, Loess Plateau, and Inner Mongolian Plateau, covering 35.3% of Northern China, highlighting enhanced vegetation growth in these regions. However, in Northwestern Xinjiang, Northeastern China, and parts of the QTP, significant negative correlations indicated that precipitation might inhibit vegetation growth, as shown in Figure 6d.  
Figure 5: Trends in gross primary productivity (GPP) (**a**) and their statistical significance (**b**) across the region’s vegetation.  
In most ecological restoration areas, temperatures showed an upward trend, with only a slight decrease observed in the Tarim Basin and southern Loess Plateau (Figure 6e). Figure 6f shows that approximately 77.1% of the study area exhibited a positive correlation between temperature and GPP, mainly in the Northeastern Plain, the QTP, and certain areas of the northern Loess Plateau. The QTP, Tianshan Mountains, and Northeastern Plain displayed significantly higher correlations, indicating that higher temperatures favored GPP growth in 6.2% of the study region. In contrast, negative correlations were observed in 22.9% of the area, particularly in the southern Loess Plateau and parts of the Inner Mongolian Plateau, suggesting that rising temperatures may hinder GPP growth and vegetation development in these regions.