## 3 Results
### Spatiotemporal Variations of GPP and WUE
Figure 3: Spatial distribution of (**a**) GPP (units: gC\(\cdot\)m\({}^{-2}\)-yr\({}^{-1}\)) and (**c**) WUE (units: gC\(\cdot\)m\({}^{-2}\)-mm\({}^{-1}\).yr\({}^{-1}\)) variation trends during 2001–2021. (**b**,**d**) represent spatial distribution of GPP and WUE \(CV\). Increased\({}^{\star}\) Decreased\({}^{\star}\): indicates the regions of significant increase or decrease (\(p<0.05\)). Figure 4: Temporal trends of GPP and WUE for different arid-humid zones across China from 2001 to 2021. (**a**,**c**) represent the trend of annual average GPP (units: gC\(\cdot\)m\({}^{-2}\).yr\({}^{-1}\)) and WUE (units: gC\(\cdot\)m\({}^{-2}\).mm\({}^{-1}\).yr\({}^{-1}\)) in different arid-humid zones. Significant changes (\(p<0.05\)) are indicated in the figure. (**b**,**d**) represent the area percentage with increasing or decreasing trends of GPP and WUE in different arid-humid zones and the average \(CV\) values of both. Increased* Decreased*: indicates the change of GPP or WUE reached a significant level (\(p<0.05\)). Figure 5: Temporal trends of GPP and WUE for different vegetation types across China from 2001 to 2021. (**a**,**c**) indicate the trends of annual average GPP (units: gC\(\cdot\)m\({}^{-2}\).yr\({}^{-1}\)) and WUE (units: gC\(\cdot\)m\({}^{-2}\).mm\({}^{-1}\).yr\({}^{-1}\)) in different vegetation types. Significant changes (\(p<0.05\)) are indicated in the figure. (**b**,**d**) represent the area percentage with increasing or decreasing trends of GPP and WUE in different vegetation types and the average \(CV\) values of both. Increased* Decreased*: indicates the change of GPP or WUE reached a significant level (\(p<0.05\)). Similar to GPP, WUE also exhibited an increasing trend in all arid-humid zones (Figure 4c), but showed a slightly increased value due to the smaller area proportion of WUE increasing regions in each aridity gradient compared to GPP (Figure 4d), which corresponded to the spatial trend of Figure 3c. Among the vegetation types (Figure 5c), WUE of forest, cropland and grassland showed increasing trends (0.0013, 0.0028, and 0.0016 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\cdot\)yr\({}^{-1}\), respectively). The three vegetation types occupied most of the area in the humid, semi-humid and semi-arid zones, which caused the rising values of WUE in these three regions (0.0015, 0.0022, and 0.0014 gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\cdot\)yr\({}^{-1}\), respectively), to be extremely consistent with these three vegetation types. The area proportion of shrubland and wetland WUE decreasing regions was higher than increasing regions, which led to a national decreasing trend in their WUE (Figure 5c,d). The \(CV\) of GPP and WUE gradually increased from the humid zone to the arid zone (Figure 4b,d). Judging from the spatial distribution of GPP \(CV\) (Figure 3b), although GPP increased significantly at the national level, the \(CV\) of GPP was generally low (0.13), which indicated that there was no large fluctuation in GPP during 2001-2021. The regions with relatively high \(CV\) in GPP were mainly concentrated in the central-eastern part of the semi-arid zone, which may be related to the implementation of national ecological restoration projects. The spatial distribution of WUE \(CV\) in Figure 3d showed that the regions with large WUE fluctuation were mainly located in the southwestern part of the semi-humid zones of China. The average \(CV\) of WUE on the national scale was lower (0.11) than GPP. Among different vegetation types, wetland exhibited higher \(CV\) values for GPP and WUE (Figure 5b,d).