## 3 Results
### Spatial Trends in Different Seasons  
#### 3.2.1 Spatial Distribution Characteristics of ET and GPP  
There was a consistent seasonal southward trend in GPP and ET from the northeast to the southwest (Figure 5a-f). It is clear that the high values of GPP and ET were concentrated in the northeastern region of the research area. Summer displayed greater maximum values of GPP and ET (5.634-699.50 g C m\({}^{-2}\) d\({}^{-1}\), 5.946-494.999 mm) than spring and fall. The southern part of the research area was characterized by low GPP and ET values because of the region's lower mean annual temperature and lower mean annual precipitation values. 2.2 Characteristics of the Distribution, as Well as the General Trend of Change, of the Yearly Mean Value of eWUE  
There were obvious spatial differences in eWUE in different seasons in Inner Mongolia, and the variation ranges were 0.130-4.012 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O, 0.416-4.147 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O and 0.083-2.531 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O, respectively. The spatial distribution pattern of eWUE in spring, summer and autumn was high in the northeast and low in the southwest (Figure 6a-c), and the high-value areas were mainly concentrated in the middle and small undulating mountainous areas in the northeast and the Hetao Plain in the west. The low-value areas were located in the plain crops and grasslands in the central and northern regions and the mountain forest regions in the northeast. While there was an overall decreasing tendency in eWUE across Inner Mongolia's four distinct seasons, there was also evidence of an upward trend in specific regions. Eighteen percent (18.36%) of the areas exhibited an increasing trend, and twenty-nine percent (29.31%) showed a declining trend in the spring. It can be shown in Figure 6d that the general geographical difference in eWUE in Inner Mongolia in spring was not statistically significant, with the rising areas scattered in sections of the northeastern part of the research area. Mainly in the study's central and southern regions, summer temperatures rose in 28.24% of the areas, fell in 69.36% of the areas and remained stable in 78.65% of the areas, with all of the changes being statistically significant at the \(p<0.05\) level (Figure 6e). In total, 66% of the regions, mostly in the central and southwestern sections of the research area and some parts of the northeastern region, passed the significance (\(p<0.05\)) test in the fall, with 33.64% and 42.18% of the regions showing an increasing trend and a downward trend, respectively (Figure 6f). Figure 5: Distribution characteristics of the multi-year mean values of ET and GPP in Inner Mongolia. (**a–c**) GPP for spring, summer and autumn, (**d–f**) ET for spring, summer and autumn. The results showed that, in DNF and GRA, the mean eWUE in spring and summer was significantly higher than that in autumn. In CRO, DBF, MF, SA and WSA, the mean eWUE in summer was significantly higher than that in spring and autumn (Figure 7). In spring and summer, the average eWUEs of DNF were the highest--2.163 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O and 2.165 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O, respectively--which were significantly higher than those of DBF and MF forest types (\(p<0.05\)); the average eWUE of SA was the lowest, being only 1.676 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O, which was significantly lower than other vegetation types (\(p<0.05\)). However, in autumn, the average eWUE of GRA was the smallest, which was 0.739 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O. In summer, the eWUE size order of each vegetation type was DNF (2.165 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O) > GRA (2.101 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O) > MF (2.045 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O) > WSA (2.031 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O)> DBF (1.744 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O) > CRO (1.715 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O) > SA (1.676 g C\(\cdot\)kg\({}^{-1}\) H\({}_{2}\)O).