## 1 Introduction
This behavior can be described as decoupling between An and Tr under heat stress. It is assumed that this is a plant strategy to reduce the adverse effects of excessive temperature on plants by cooling the air temperature above the canopy through evaporation [28]. Low temperature reduces photochemical efficiency, and thus, limits the rate of CO\({}_{2}\) assimilation. It can also lead to photoinhibition [29], which affects the quantum yield of photosystem II (PSII) by disrupting the photosynthetic mechanisms of plants [30]. High temperatures will inhibit An [31] and increase respiration [32], making plants vulnerable to heat stress [33]. Thus far, evidence for this uncoupling between An and Tr has come from experiments with individual trees, either through the investigation of inter-material conduction at the leaf scale [34; 35] or whole-tree gas exchange [28]. These studies suggest decreased An under extreme temperatures, but a continually rising Tr. Most of these studies report decoupling phenomena involving decreased An and sustained increases in Tr due to drying soils and rising temperatures. In the Ball-Berry model, leaf stomatal conductance has a linear relationship with An. When the ambient temperature and humidity remain unchanged, this indicates that the stomatal conductance of plant leaves is directly proportional to An and inversely proportional to the difference between the concentrations of CO\({}_{2}\) inside and outside the leaf stomata. However, the An of plants has an unknown quantity. To reveal the relationship between leaf stomatal conductance and light intensity, the Ball-Berry model must be coupled with a light response model of plant leaves to obtain the relationship between the two. However, the relationship between stomatal conductance and light intensity varies depending on the coupled light response model [36; 37; 38; 39]. With the continuous development of evapotranspiration research, domestic and foreign scholars have put forward different evapotranspiration estimation models, among which the Penman-Monteith equation is currently recognized as an evapotranspiration estimation model with high accuracy, strong applicability, and high reliability [40]. At present, there are few experiments on the synergistic effects of warming and drought on wheat growth and yield formation. In addition, there are many studies on the diurnal characteristics of An and Tr in the leaves of various crops. However, these studies have not focused on the coupling relationship between warming-induced water deficit and the An and Tr in winter wheat. Further exploration of the coupling mechanism of An and Tr in winter wheat under warming and drought stress conditions also has important implications for understanding the environmental adaptability and productivity of wheat under future climate change. In arid and semi-arid regions, such as the North China Great Plain, soil moisture status plays an important role in crop response to climate change. However, the effects of water supply on stomatal conductance, An, Tr, and the fitting effect of measured and simulated values of wheat under climate change are still unclear. Therefore, we hypothesized that climate warming and drought have effects on crop photosynthesis. To improve the ability of crops to cope with climate change, a winter wheat climate warming and drought stress experiment was conducted using a lysimeter under a rain shelter. Based on the Ball-Berry, Jarvis, and Penman-Monteith models, stomatal conductance, An, and Tr were calculated using three sets of mathematical model formulas, and then, the measured values were observed using an LI-COR 6400 XT photosynthometer. The effects of increasing temperature and drought on the stomatal conductance, An, and Tr of winter wheat, and the fitting effect of measured and calculated values of winter wheat, were further studied.