## 1 Introduction
### The Current State of Investigation on Photosynthesis and COS Assimilation  
As a trace gas [32], the largest source of the COS atmospheric budget is the oceans of the Southern Hemisphere and the low latitude regions [33; 34], as well as anoxic soils [35; 36; 37; 38; 39; 40], i.e., directly from sulfur-containing organic matter or indirectly transferred from dimethyl sulfide (DMS) and carbon disulfide (CS\({}_{2}\)) [41; 42; 43; 44]. Meanwhile, anthropogenic activities are the largest influencing factor of regional COS emission [45; 46; 47; 48; 49]. Among the whereabouts of atmospheric COS, vegetation photosynthesis plays a major role in tropospheric COS consumption [50]. From the process point of view, when catalyzed by the enzyme carbonic anhydrase (CA), COS can be irreversibly fixed in plants and soil (COS + H\({}_{2}\)O \(\rightarrow\) HCOOS\({}^{-}\) + H\({}^{+}\)) [37; 51; 52; 53; 54; 55; 56]. In terms of the correlation between the photosynthetic hydrolysis rates of COS and CO\({}_{2}\)[57; 51; 52; 53; 54; 55; 56] or the temporal dynamics of the proportional volume mixing ratio [32; 41; 42; 57], the canopy assimilation rate of COS is correlated with that of CO\({}_{2}\). Furthermore, unlike CO\({}_{2}\), COS cannot be emitted through respiration. The COS flux is employed as an indicator of GPP in ecosystems [58; 59; 60]. Stomatal conductance (g\({}_{\rm s}\)) can also be estimated by extrapolating the stomatal conductance of H\({}_{2}\)O (g\({}_{\rm s,H2O}\)) from the stomatal conductance of COS (g\({}_{\rm s,COS}\)) [61; 62; 63]. Based on laser spectroscopy technology [64], high-frequency observations of trace gases make it possible to measure the chamber-based or the EC flux COS [65; 66; 67]. At the regional scale, when using the processes-based land surface models (LSMs), such as SiB 4 and ORCHIDEE [68; 69; 70], to estimate the spatiotemporal variations of GPP [68; 71; 69; 72; 73], transpiration and g\({}_{\rm s}\)[54; 74; 55], researchers take the atmospheric COS mixing ratio data of observation networks [58] and quantitative remote sensing as the input variables [76; 77; 78; 79; 80]. Global studies take the carbon assimilation systems, such as Carbon Tracker-Langrange, to recognize the sources and sinks of COS [71; 81]. Recently, scientists are also making efforts to identify the missing source and sinks of global atmospheric COS [60; 82; 83; 61; 62; 63; 64]. It is urgent to precisely formulate the regulation mechanism of canopy COS assimilation, as well as the linkage between canopy COS flux (F\({}_{\rm C,COS}\)) and GPP. The following field observations have studied the relationship between environmental factors and COS assimilation. Site observation of bryophytes found that the biological fixation of COS is mostly regulated by meteorological factors [85]. In plant leaf photosynthesis, during hydrolysis, the catalysis of COS by the CA enzyme is light-independent [37; 41] and more efficient than that of CO\({}_{2}\)[86]. During the light response of photosynthesis, CO\({}_{2}\) is preferentially catalyzed by RuBisCO over COSby a factor of 110 [51; 87]. Moreover, the catalytic efficiency of the CA enzyme, which is highly abundant, exceeds that of RuBisCO overall [88; 89; 37; 86]. At the leaf scale, stomata are not only the gateway for photosynthetic CO\({}_{2}\) assimilation but also the vapor flux in transpiration. At the same time, COS is assimilated through the diffusive pathway (e.g., the leaf boundary layer, stomata and mesophyll). From the process perspective, environmental conditions (e.g., light, temperature, leaf moisture conditions and the CO\({}_{2}\) concentration in the leaf boundary) have an important role in the conductance of both the stomata and mesophyll [90]. In response to leaf drought, to protect the mesophyll cells from excessive water loss, abscisic acid (ABA) is transferred to the stomata by the catheter sap flow [91], which stimulates the striction of guard cells and the stomata close.