## 3 Results
### Response Mechanism Analysis  
#### 3.4.1 Results of Partial Correlation Analysis  
The NPP, ET, and WUE showed significant variation trends at different 100 m elevation gradients, with NPP and WUE exhibiting similar trends across these gradients. To standardize the elevation gradient intervals, this study divided the elevation into three zones: <3000 m, 3000-3700 m, and >3700 m. The responses of NPP, ET, and WUE to factors such as Prec, Temp, SM, ST, VPD, and PAR were analyzed, as shown in Figure 11.  
The results showed that the partial correlation relationships between various factors and NPP differed across elevation zones. Below 3000 m, only VPD had a negative partial correlation with NPP, with partial correlation coefficients ranging from \(-0.40\) to \(-0.20\). Prec, Temp, SM, sST, and PAR all showed positive correlations with NPP, with the correlation between Prec and NPP being weak, having a partial correlation coefficient around 0.1. Below 3000 m, the positive correlation between SM and NPP was the strongest, with partial correlation coefficients ranging from 0.30 to 0.45. The positive correlations between ST  
Figure 10: Distribution characteristics of vegetation NPP, ET, and WUE with elevation: (a) NPP, (b) ET, (c) WUE. and PAR with NPP were somewhat weaker. Between 3000 m and 3700 m, the relationship between Prec and NPP became less pronounced, with partial correlation coefficients ranging from \(-0.10\) to 0.05. The positive correlation between ST and NPP was the strongest, with a partial correlation coefficient around 0.60. The positive correlation between SM and NPP was weakened. The partial correlation between VPD and NPP changed to a positive correlation, with a correlation coefficient of approximately 0.15. The relationships between Temp and PAR with NPP showed no significant changes. As the elevation increases, when the elevation exceeds 3700 m, thermal factors primarily influence the NPP of vegetation. The partial correlation coefficient between Temp and NPP reached around 0.35, and the relationship between ST and NPP remained the strongest, with a partial correlation coefficient of about 0.50. The effects of Prec and SM on NPP became less significant. VPD showed a notable positive correlation with NPP, with a correlation coefficient around 0.20. In summary, there were indeed differences in the relationships between various factors and NPP across different elevation zones. As the elevation increases, the relationship between Temp and NPP strengthens; ST showed an initial increase followed by a decrease, and the relationship between VPD and NPP shifted from negative to positive, as shown in Figure 11a. The partial correlation relationships between ET and various factors also differed across different elevation gradients. Prec, Temp, SM, ST, and PAR all showed a positive correlation with ET at different elevation zones, while VPD was negatively correlated with ET. Below 3000 m, the partial correlation coefficient between Prec and ET was around 0.13. Between 3000 and 3700 m, the median of the partial correlation coefficient between Prec and ET decreased. Above 3700 m, the interquartile range became smaller, and the partial correlation coefficient between Prec and ET became uniform across this elevation zone. The partial correlation between Temp and ET was positive across all elevation zones, indicating that with an increase in temperature, both soil evaporation and vegetation transpiration intensify. However, above 3700 m, the median of the box plot was lower, which may be due to the limitation of water-related factors in high-altitude areas, restricting ET. The partial correlation coefficient between SM and ET was positive across all elevation zones, indicating that an increase in SM promoted ET. Below 3000 m, the partial correlation coefficient was relatively low and more dispersed, suggesting that the influence of SM on  
Figure 11: Correlation of vegetation NPP, ET, and WUE with water, heat, and light factors at different elevation gradients: (**a**) vegetation NPP, (**b**) ET, and (**c**) WUE.