## 3 Results
### Contribution of Each Vegetation Type to GPP, ET, and WUE IAV  
The primary vegetation types in Inner Mongolia are coniferous forests (6.23%), broadleaf forests (7.75%), meadow steppe (12.77%), typical steppe (23.36%), desert steppe (17.97%), shrubs (6.85%), cropland (13.76%), and sand land vegetation (11.31%). The annual average values of GPP, ET, and WUE for different vegetation types are presented in Figure 5. The relatively highest GPP values were found in broadleaf forests, converious forests, and meadow steppe in the study area, with values exceeding 800 gC m\({}^{-2}\) yr\({}^{-1}\). Among them, broadleaf forests showed the highest value, with a mean of 938.36 gC m\({}^{-2}\) yr\({}^{-1}\), followed by coniferous forests, meadow steppe, shrubs, cropland, typical steppe, and sand land vegetation. On the contrary, the desert steppe showed the lowest GPP (94.42 gC m\({}^{-2}\) yr\({}^{-1}\)). Regarding ET, coniferous forests showed the highest value at 439.74 mm yr\({}^{-1}\), followed by broadleaf forests, meadow steppe, shrubs, cropland, sand land vegetation, and typical steppe, with their average values exceeding 290 mm yr\({}^{-1}\), while desert steppe showed the lowest value at 204.26 mm yr\({}^{-1}\). Broadleaf forests showed the highest WUE value, with an average of 2.26 gC m\({}^{-2}\) mm\({}^{-1}\), while desert steppe showed the lowest WUE value at 0.46 gC m\({}^{-2}\) mm\({}^{-1}\). The mean values of WUE for different vegetation types followed the order: broadleaf forest > coniferous forest > meadow steppe > shrub > cropland > typical steppe > sand land vegetation > desert steppe.  
Figure 5 depicts the contribution of each vegetation type to GPP, ET, and WUE IAV. The contribution of each vegetation type to GPP, ET, and WUE IAV showed some variability. We discovered that typical steppe contributed the most (169.89%) to GPP IAV from 2001 to 2020, followed by cropland ecosystem (164.18%), and they are mostly found in the southeast and western rivers regions. The area of the shrub only accounts for 6.85% of the total area, but they make a great contribution to GPP IAV in arid and semi-arid zones, with a value of 143.69%. The broadleaf forest and sand land vegetation contributed 75.35% and 71.57% to GPP IAV, respectively. The desert steppe ecosystems cover far more area than shrubs and sand land vegetation, but they contributed only 31.51%. Among all vegetation types, only coniferous forest ecosystems contribute negatively to GPP IAV, with a value of \(-\)36.28%. The typical steppe contributed the most (141.09%) to ET IAV and was primarily distributed in the western Hulun Buir and Xilin Gol regions. The desert steppe ecosystems were the second largest contribution to ET IAV (129.70%), followed by cropland (117.87%), shrubs (113.44%), and sand land vegetation (107.94%). By contrast, the meadow steppe, broadleaf forest, and coniferous forest ecosystems contributed the least to ET IAV, with a value of 48.70%, 37.15%, and 28.20%, respectively. More importantly, we found that typical steppe accounts for the largest fraction (193.42%) of the WUE IAV over this period, followed by cropland ecosystems contributed 106.85%. The desert steppe, shrubs, sand land vegetation, meadow steppe, and broadleaf forest ecosystems contributed to WUE IAV with 102.25%, 92.99%, 74.95%, 72.42%, and 27.27%, respectively. In contrast, we found that coniferous forest ecosystems account for the lowest fraction of the WUE IAV at \(-\)32.86%. In addition, the WUE exhibits significant fluctuation at each vegetation type, with typical steppe anomalies being the greatest compared to other vegetation types. While desert  
Figure 4: Mean values of (**a**) GPP, (**b**) ET, and (**c**) WUE in various seasons in Inner Mongolia.  
steppe anomalies are more volatile for ET, coniferous forest anomalies are more prominent for GPP (Figure 6).