# Comprehensive Effects of Atmosphere and Soil Drying on
## 3 Results
### Effect of Decoupling VPD and SWC on Vegetation Stomatal Behavior  
Figure 3 illustrates the distribution of Gs, GPP, and NPP across five vegetation types, where Gsref, GPPref, and NPPref represent the plant reference stomatal conductance, primary productivity, and net primary productivity (defined as the mean of VPD between 0.9 and 1.1 kPa), respectively. For the CRO and DBF sites, when the SWC percentile is in the 90-100% range, Gs shows a very slow increasing trend with increasing VPD compared to other SWC ranges, which may imply that extremely high SWC weakens the limiting effect of increasing VPD on Gs, and may even promote an increase in Gs in the opposite direction. Analyzing the impact of SWC on Gs across the five vegetation types reveals that there is a large difference in Gs among different SWC percentile ranges, and the difference in Gs/Gref is even greater than 1 when VPD is around 1 kPa. Overall, except for the SAV sites, the Gs of the other four vegetation types decrease with decreasing SWC, with the CRO and GRA showing the most significant SWC limitation, while the relationship between SWC and Gs in the SAV sites differs from that of other vegetation types, as Gs is almost greater in all VPD ranges when SWC is low (0-30%) than when it is high (30-70%). This phenomenon may be due to the overall low and stable SWC at the SAV sites, where slightly lower SWC may be more favorable for plant stomatal opening. Figure 2: Ranges of four variables (**a**) VPD, (**b**) SWC, (**c**) SWin, and (**d**) Ta for five PFT (CRO, DBF, ENF, GRA, and SAV) sites. The upper, middle, and lower horizontal lines represent the 75 th percentile, median, and 25 th percentile, respectively. The red dot represents the mean value, and the blue ‘+’ sign represents an abnormal value. In contrast to Gs, the GPP of the five vegetation types reflects different characteristics, with DBF, ENF, and GRA showing an overall decrease in GPP with increasing VPD, which is also affected by SWC. The GPP with a high SWC range (70-100%) in the DBF and the GRA sites is significantly larger than the low SWC range (0-15%) at various VPD values, and the difference between them gradually decreases with increasing VPD, while the ENF is less affected by SWC, with similar GPP values across all VPD ranges. The GPP variation in the CRO sites reveals that GPP does not show any obvious limitation effects in various VPD ranges, but instead increases with increasing VPD at higher SWC (90-100%), which is possibly affected by human activities, indicating that the effect of VPD limitation on GPP in CRO with different SWC conditions is not significant. The GPP variation in SAV is clearly different from the previous four vegetation types, with a general trend of increasing first and then decreasing, where GPP increases with increasing VPD when VPD is less than 2 kPa and starts to decrease when VPD is greater than 2 kPa, but is not limited by VPD in the high SWC range (90-100%). The GPP in SAV sites is also limited by SWC, where similar to Gs distribution, the GPP value in the low SWC range (0-30%) is greater than that in the high SWC range (30-50%). The comparison of NPP distribution shows that the basic characteristics are consistent with GPP distribution, indicating a strong correlation between the two. However, it is worth noting that in ENF sites, there is a trend of increasing NPP with increasing VPD in the 30-50% SWC range, and NPP in the 70-100% and 0-15% SWC ranges is very similar and significantly decreases with increasing VPD. To facilitate a more intuitive comparison of the effects of VPD and SWC on Gs, GPP, and NPP, we analyzed the variability in these three variables at various VPD and SWC percentiles (Figure 4). By dividing Gs, GPP, and NPP into 10 \(\times\) 10 grids based on every 10 th percentile of VPD and SWC, with red indicating positive changes and blue indicating negative changes, we found that the five vegetation types exhibited clear stratification in VPD and SWC.