Abstract: Aims Climate change has led to a marked increase in the frequency of extreme heat events, posing a serious threat to wheat growth. Existing studies have investigated the effects of extreme heat on the photosynthetic processes of wheat, whereas studies on its effects on leaf temperature and the underlying regulatory mechanisms remain relatively limited. Methods In this study, three widely cultivated wheat cultivars in the Jianghuai region—Nongmai 77, Nongmai 88, and Yangmai 39—were used as experimental materials. A field-based experimental platform simulating extreme heat conditions was employed, with two treatments established: normal ambient temperature (control) and extreme heat. Continuous measurements of leaf temperature, diurnal variations in stomatal conductance, photosynthetic rate, and relative chlorophyll content were conducted to elucidate cultivar-specific responses of leaf temperature and photosynthesis to extreme heat. Important findings The results showed that mean air temperature increased by 2.7 °C; however, wheat leaf temperature did not change significantly, resulting in a significant reduction in the leaf-to-air temperature difference during the extreme heat treatment. Under extreme heat conditions, the mean stomatal conductance (gs) of Nongmai 77, Nongmai 88, and Yangmai 39 increased by 59.3%, 56.7%, and 32.4%, respectively, compared with the control. Diurnal analysis indicated that the largest increases in gs occurred at 13:00 and 15:00, with increments of 67.4% and 26.1%, respectively. Under the coupled conditions of reduced radiation and elevated air temperature, extreme heat significantly increased stomatal conductance (gs) and leaf transpiration rate, suggesting that wheat may alleviate the adverse effects of high temperature on leaves by enhancing transpiration. Extreme heat had no significant effects on relative chlorophyll content or saturated photosynthetic rate, but it significantly reduced leaf-scale water use efficiency. Overall, wheat leaves exhibited strong acclimation to the extreme heat conditions examined in this study, primarily by enhancing transpiration and increasing latent heat flux to maintain relatively stable leaf temperature and photosynthetic rate, albeit at the cost of increased water consumption and reduced water use efficiency.

Key words: Heat, wheat, leaf temperature, photosynthesis, stomatal conductance