## 3 Results  
### Spatial and Temporal Characteristics of Vegetation CUE and WUE  
From 2001 to 2023, the average annual total values of GPP, NPP, and ET in the NMR were 1821.28 g C\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\), 846.01 g C\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\), and 1025 mm\(\cdot\)a\({}^{-1}\), respectively. These three vegetation indicators exhibited similar spatial distribution patterns, displaying a trend of \"lower values in the northwest and higher values in the southeast\". All three indicators exhibited an upward trend throughout the study period, with GPP, NPP, and ET increasing at rates of 8.899 g C\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\), 5.121 g C\(\cdot\)m\({}^{-2}\)\(\cdot\)a\({}^{-1}\), and 1.864 mm\(\cdot\)a\({}^{-1}\), respectively (Figure 2). These results highlight the favorable vegetation growth conditions in the NMR and the significant improvements in ecological restoration outcomes.  
The NMR's CUE and WUE experienced a notable decrease (\(p<0.05\)) between 2001 and 2023, with average values of 0.47 and 0.82 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), respectively. The annual rates of reduction were 0.0014 for CUE and 0.0022 for WUE, indicating that the year-to-year variations in CUE and WUE exhibited relative stability over the study duration. This study revealed an overall significantly declining trend in both CUE and WUE (\(p<0.05\)), caused by the increases in GPP and ET outpacing that of NPP, leading to a reduction in the long-term averages of CUE and WUE in the NMR from 2001 to 2023. This steadiness was impacted by notable growth in GPP and ET (\(p<0.01\)), alongside a non-significant increase in NPP (Figure 2). The minimum CUE value was noted in 2014, whereas the maximum was in 2001. For WUE, the peak value appeared in 2004, and the lowest was recorded in 2019. The CUE and WUE across the study region displayed marked spatial variability (Figure 3), generally reflecting a trend of \"lower in the northwest and higher in the southeast\". Areas where CUE exceeded 0.5 made up 50.11% of the entire study region, while approximately 49.89% had a CUE below 0.5. For WUE, 49.91% of the area had values below 0.8, 38.49% fell between 0.8 and 1.0, and approximately 11.60% exceeded 1.0. Overall, among different vegetation types, the mean CUE was found to be highest in shrublands and lowest in forests, whereas the mean WUE was highest in forests and lowest in shrublands (Figure 4). The variation in CUE among different vegetation types was relatively small, with mean values ranking as follows: shrubland (0.570) > cropland (0.528) > grassland (0.502) > forest (0.440). In contrast, the mean WUE values varied more notably among vegetation types, ranking as follows: forest (0.831 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) > grassland (0.818 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) > cropland (0.776 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)) > shrubland (0.624 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\)). The variations in CUE across various vegetation types were relatively small, and areas where CUE exceeds 0.5 accounted for 50.11% of the study region. The highest average CUE was found in shrubland (0.570), while the lowest was in forest (0.440), with a difference of 0.130. The WUE demonstrated considerable variation across different vegetation categories, highlighting significant distinctions in how various vegetation types utilize water resources. In particular, forested regions exhibited the highest WUE, reaching 0.831 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), whereas shrubland showed the lowest WUE at 0.624 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\), resulting in a discrepancy of 0.207 g C\(\cdot\)m\({}^{-2}\cdot\)mm\({}^{-1}\) between the highest and lowest values.  
Figure 2: Variation in (**a**) vegetation CUE and WUE from 2001 to 2023 in the NMR. (**b**) NPP, GPP, and ET from 2001 to 2023 in the NMR. Statistical significance is indicated as follows: * for \(p<0.05\) and ** for \(p<0.01\).