# Comprehensive Effects of Atmosphere and Soil Drying on
## 5 Conclusions  
This research analyzed hourly meteorological flux data from 36 flux sites across five vegetation types worldwide (CRO, DBF, ENF, GRA, SAV) to investigate how variables such as VPD and SWC affect vegetation stomatal behavior and productivity for different types of vegetation. It was found that these variables have a significant impact on ecosystem WUE and CUE, indicating the importance of understanding how they affect ecosystems. The following conclusions were drawn:  
1. High VPD coupled with low SWC can restrict plant stomatal conductance, GPP, and NPP. However, in some vegetation types (CRO, DBF), high soil moisture content can offset the negative impact of high VPD, while low SWC limits vegetation stomatal conductance. Interestingly, in SAV, lower SWC levels (percentiles 0-30%) can lead to higher stomatal conductance and GPP than higher SWC levels (percentiles 30-70%). For certain PFTs, higher soil moisture levels can alleviate the limitation caused by high VPD and even partially promote GPP and NPP as VPD increases. Notably, there is an anomalous increase in NPP in the ENF vegetation type when soil moisture percentiles range between 30 and 50%, leading to a corresponding increase in CUE as soil moisture content increases with VPD.
2. Vegetation stomatal conductance and productivity have a direct impact on both WUE and CUE. Across the various vegetation types, an increase in VPD generally results in an increase in WUE, while the influence of SWC on WUE is less clear. Moreover, specific analyses reveal that the effect of VPD on WUE is more significant than that of SWC. The changes in WUE due to increasing VPD occur at an average WUE value of approximately 50 \(\upmu\)mol/mol, with the ENF vegetation type being the most affected at 70 umol/mol. Conversely, the changes in WUE due to decreasing SWC occur at an average WUE value of about 30 umol/mol.
3. The CUE of the CRO, DBF, ENF, and GRA vegetation types decreases as VPD increases, whereas the impact of SWC on these four types is relatively insignificant, with only a \(-0.05\) umol/umol total change. In contrast, the SAV vegetation type's CUE is affected differently by VPD and SWC, displaying an ascending tendency in CUE changes that are dominated by the rise in VPD and decline in SWC. This indicates that a decrease in SWC and increase in VPD foster the enhancement of CUE in the SAV vegetation type to some extent.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/w15091675/s1](https://www.mdpi.com/article/10.3390/w15091675/s1)]([https://www.mdpi.com/article/10.3390/w15091675/s1](https://www.mdpi.com/article/10.3390/w15091675/s1)), Table S1: Station ID, latitude (\({}^{\circ}\)), longitude (\({}^{\circ}\)) and plant functional type of the 36 Selected flux stations.  
Conceptualization, Y.T. and Z.X.; methodology, [PERSON]; writing--original draft preparation, Y.T., X.X. and Z.X.; writing--review and editing, Z.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Regional Innovation Development Joint Project of National Natural Science Foundation of China (U21A2021), National Natural Science Foundation of China (U2040212), and China Three Gorges Corporation Research Project (Contract No: 202103429, 202203050).  
The fluxnet data are available in the following website: [[http://fluxnet.fluxdata.org/data/Fluxnet2015](http://fluxnet.fluxdata.org/data/Fluxnet2015) dataset/]([http://fluxnet.fluxdata.org/data/Fluxnet2015](http://fluxnet.fluxdata.org/data/Fluxnet2015) dataset/), accessed on 16 June 2020.  
The authors would like to express their appreciation to the fluxnet website for sharing the observing flux dataset for the research and to the editor and the anonymous reviewers, who provided very helpful comments to improve the manuscript.  
The authors declare no conflict of interest.