## 3 Results
### Changes in GPP and WUE for Each Vegetation Type in Arid-Humid Zones  
To further investigate the variation of GPP and WUE along the aridity gradient for all vegetation types, we conducted statistical analyses on the average GPP and WUE values, trends, and \(CV\) for all vegetation types in four arid-humid zones from 2001 to 2021, as shown in Figures 6 and 7, and Tables 1 and 2. In each of the arid-humid zones, GPP and WUE values remained high for forest and cropland, and maintained a stable distribution pattern for grassland, while wetland and shrubland varied dramatically. In the semi-humid zone, the values of GPP and WUE in the shrubland were significantly higher than other vegetation types and also exhibited a higher distribution compared to the other three arid-humid zones (Figures 6b and 7b). In the arid and semi-arid zones, the GPP and WUE of wetland also showed the same distribution pattern. But this phenomenon is not evident in Figure 2 due to the relatively small area of both on a national scale. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**GPP-Trend/\(CV\)** & **Humid** & **Semi-Humid** & **Semi-Arid** & **Arid** \\ \hline Forest & 7.94/0.103 & 7.69/0.111 & 5.65/0.096 & 4.15/0.158 \\ Shrubland & 1.62/0.251 & 14.78/0.126 & 0.49/0.112 & 1.97/0.221 \\ Grassland & 3.53/0.153 & 5.36/0.151 & 4.35/0.163 & 2.84/0.179 \\ Weltand & 1.35/0.182 & 3.89/0.219 & 4.54/0.108 & 3.69/0.124 \\ Cropland & 8.42/0.102 & 9.31/0.121 & 7.21/0.123 & 5.06/0.122 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Trends (units: gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\cdot\)yr\({}^{-1}\)) and \(CV\) of GPP for each vegetation type in different arid-humid zones from 2001 to 2021. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**WUE-Trend/\(CV\)** & **Humid** & **Semi-Humid** & **Semi-Arid** & **Arid** \\ \hline Forest & 0.001/0.091 & 0.002/0.088 & 0.001/0.087 & \(-\)0.001/0.161 \\ Shrubland & \(-\)0.002/0.142 & \(-\)0.001/0.081 & 0.001/0.136 & \(-\)0.001/0.202 \\ Grassland & 0.002/0.155 & 0.001/0.132 & 0.002/0.132 & 0.002/0.136 \\ Wetland & \(-\)0.001/0.199 & 0.006/0.203 & \(-\)0.003/0.109 & \(-\)0.002/0.103 \\ Cropland & 0.002/0.092 & 0.003/0.086 & 0.001/0.086 & 0.001/0.094 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Trends (units: gC\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\cdot\)yr\({}^{-1}\)) and \(CV\) of WUE for each vegetation type in different arid-humid zones from 2001 to 2021. Figure 6: Distribution of GPP for different vegetation types in four arid-humid zones from 2001–2021. (**a–d**) represent the GPP distribution for each vegetation type in the humid, semi-humid, semi-arid, and arid zones. The upper, middle, and lower lines of each violin plot represent the maximum, median and minimum values, the middle rectangle indicates the 25%-75% quantile. The width of the violin plot represents the intensity of the distribution of values. Figure 7: Distribution of WUE for different vegetation types in four arid-humid zones from 2001–2021. (**a–d**) represent the WUE distribution for each vegetation type in the humid, semi-humid, semi-arid, and arid zones. The upper, middle and lower lines of each violin plot represent the maximum, median and minimum values, the middle rectangle indicates the 25%-75% quantile. The width of the violin plot represents the intensity of the distribution of values. Table 1 reveals that the GPP of all vegetation types in each arid-humid zones exhibited an increasing trend, among which shrubland in the semi-humid zone showed the largest GPP growth values, and wetland GPP also showed relatively high growth values in the arid and semi-arid zones. In all arid-humid zones, the GPP of forest and cropland generally increased significantly, with the GPP of cropland increasing to a greater extent in all but the arid zone, while forest was concentrated in the humid and semi-humid zones. Similarly, the grassland GPP maintained a steady increase across the arid-humid zones.