## 5 Conclusions  
During plant photosynthesis and COS assimilation, light and water conditions co-regulated the stomata and LRU. Overall, at diurnal scales, \(\mathrm{F_{C,COS}}\) was controlled by the stomata and was decreased by water shortage in non-wetting biomes; at the same time, the leaves were exposed to increased \(\mathrm{C_{a,COS}}\). However, under variations in the environmental conditions, a three-step response occurred in \(\mathrm{F_{C,COS}}\). First, slightly increased light increased the \(\mathrm{g_{s}}\), as well as the COS emission from the canopy gap; then, \(\mathrm{F_{C,COS}}\) was decreased. Second, when the stomata were opening, since the subcanopy emission of COS and the enzyme CA catalysis rate of COS exceed \(\mathrm{CO_{2}}\), a \(\mathrm{C_{a,CO_{2}}}\) increase of 10 to 40 \(\mathrm{\SIUnitSymbolMicro m^{-2}~{}s^{-1}}\) was a compensation point for COS assimilation, at which point, \(\mathrm{F_{C,COS}}\) was the lowest. Third, the stomata closed under both high light intensity and high temperatures, and \(\mathrm{F_{C,COS}}\) was decreased as well. Although this study provided no evidence of the correlation between the LRU and \(\mathrm{g_{s}}\), they were shown to be regulated by the variations in environmental conditions in opposite ways, at least in MXF and \(\mathrm{CP_{C3}}\). Moreover, the LRU decreased under slightly increased light and atmospheric drought. The LRU saturation points of \(\mathrm{C_{a,COS}}\) and \(\mathrm{C_{a,CO_{2}}}\) were observed when \(\mathrm{\Delta C_{a,COS}}\approx 13\) ppt or \(\mathrm{\Delta C_{a,CO_{2}}}\approx-18\) ppm. In further studies, we will formulate the quantitative model of the LRU regulation mechanism based on the above-mentioned conclusion using \(\mathrm{g_{s}}\), \(\mathrm{C_{a,COS}}\), \(\mathrm{C_{a,CO_{2}}}\), light and water conditions.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/su14052840/s1](https://www.mdpi.com/article/10.3390/su14052840/s1)]([https://www.mdpi.com/article/10.3390/su14052840/s1](https://www.mdpi.com/article/10.3390/su14052840/s1)), Table S1: The changes in environmental conditions as well as the variations of Hedges'd and Ln(RR) among different dependent variables (e.g., LRU, \(\mathrm{g_{s}}\), \(\mathrm{F_{C,COS}}\), \(\mathrm{F_{C,CO_{2}}}\)) and different groups; Table S2: The studies collected in this meta-analysis; Table S3: Dependent variables (e.g., LRU, \(\mathrm{g_{s}}\), \(\mathrm{F_{C,COS}}\), \(\mathrm{F_{C,CO_{2}}}\)) and related environmental conditions collected in each study; Section S1: Studies collected in this meta-analysis; Section S2: The abbreviations used in this study.  
**Author Contributions:** Conceptualization, S.W., L.W. and J.C.; Data curation, P.W. and J.C.; Formal analysis, P.W.; Investigation, P.W., L.W., J.C., L.M. and X.W.; Methodology, P.W., L.M. and X.W.; Project administration, S.W. and L.W.; Resources, P.W. and K.Z.; Software, P.W., X.W. and Y.L.; Validation, B.C., L.M. and Y.L.; Visualization, P.W., Y.L. and K.Z.; Writing--original draft, P.W.; Writing--review and editing, S.W., B.C., M.A. and J.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was finally supported by the Scientific Instrument Developing Project of the Chinese Academy of Sciences, Grant No. YJKYQ20190042, and the National Key Research and Development Program of China No. 2017 YFC0503803.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data collected in this article is within the \"Supplementary Materials\" document.  
**Acknowledgments:** We are grateful to the scientists who contributed to the global database used in this meta-analysis.  
**Conflicts of Interest:** The authors declare no conflict of interest.