## 2 Materials and Methods  
### Data Preparation  
We used \(\text{F}_{\text{C,COS}}\), \(\text{F}_{\text{C,CO}2}\) and the relevant environmental conditions to explain the mechanism of COS assimilation during photosynthesis and the LRU regulation mechanism based on stomata. During the data preparation, we collected studies published during 1985-2020 from Google Scholar and Web of Science, which simultaneously observed \(\text{g}_{\text{s}}\), \(\text{F}_{\text{C,COS}}\), \(\text{F}_{\text{C,CO}_{2}}\), environmental conditions and the simulated LRU [14; 51; 113; 114; 115; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129]. According to the PRISMA statement of systematic reviews and meta-analyses, when retrieving these studies, we used measurement, photosynthesis and \(\text{g}_{\text{s}}\) as the keywords, and then selected 228 studies. Then, we used measurement, photosynthesis and COS as the keywords, and then selected 58 studies. In the intersection of the two folders there were 25 studies that simultaneously observed photosynthesis, COS and \(\text{g}_{\text{s}}\). Then, to constrain the uncertainty caused by the temporal variation of observations from instruments and the parameters, we paid no consideration to the belowground parts [90] and just chose measurements of  
Figure 1: Schematic diagram of COS and \(\text{CO}_{2}\) assimilation during leaf photosynthesis. The diffusion processes of COS and \(\text{CO}_{2}\) are generalized from Section 1.2. The current state of investigation on photosynthesis and COS assimilation by us. Blue font characters are the key environmental conditions we filtered from the literature. In the corresponding physiological processes, they act as regulators. The source literature is as follows: light intensity [37; 41; 51; 86; 87; 90], rH [61; 62; 63; 85; 90; 91; 92; 93; 94; 106; 107; 108; 115], VPD [102; 103; 104; 105] and \(\text{C}_{\text{a,COS}}\) and \(\text{C}_{\text{a,CO}_{2}}\)[37; 41; 50; 51; 52; 53; 54; 55; 56; 60; 73; 87; 97; 98; 109]. leaves. Ultimately, 22 datasets from 15 sites were chosen for this meta-analysis. During measurements of the leaf gas exchange and g\({}_{\mathrm{s}}\), these studies also measured relevant environmental conditions. We collected four categories of environmental conditions, and light conditions were represented by light intensity (\(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)) or photosynthetic active radiation (PAR, \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)), temperature conditions were represented by the canopy or soil temperature (\({}^{\circ}\)C) and water conditions were represented by rH (%) and VPD (Pa). Meanwhile, the atmospheric COS and CO\({}_{2}\) concentrations were represented by C\({}_{\mathrm{a,COS}}\) (ppt) and C\({}_{\mathrm{a,CO_{2}}}\) (ppm). Raw data were acquired from the tables, figures and appendixes of the publications using Engauge Digitizer (Free Software Foundation, Inc., Boston, MA, USA). Relationships between the environmental conditions and dependent variables (i.e., LRU, g\({}_{\mathrm{s}}\), F\({}_{\mathrm{C,COS}}\), and F\({}_{\mathrm{C,CO_{2}}}\)) identified in the studies were also collected for verification of the results. We filtered the search results to find studies performed over the plant photosynthetic part of terrestrial ecosystems and classified the research in previous studies on the basis of their study sites. Then, these studies were categorized into subsets of biomes on the basis of their study sites. These biomes included needle-leaf forest (NLF), broadleaf forest (BLF), mixed forest (MXF), grassland (GRA), marsh (MSH), cropland dominated by C3 plants (CPLC3) and cropland dominated by C4 plants (CPLC4) (Figure 2). In each biome group, the studies were separated according to their measurement frequencies.