Response of photosynthetic physiological characteristics of spring wheat to drought stress under high temperature conditions

To explore the mechanism of the photosynthetic physiological response of spring wheat to drought and high temperature in arid areas, field experiments were conducted at the Wuwei Desert Ecological and Agricultural Meteorological Experiment Station in Gansu Province, a typical arid area. Three treatments were established: adequate water supply (CK, soil moisture content maintained at 80% of the field capacity), drought stress starting from the vegetative growth stage (T1), and drought stress starting from the reproductive growth stage (T2). The light-response curves of photosynthetic characteristics of spring wheat leaves were determined under the leaf temperature regulation conditions of 25 ℃ (suitable temperature) and 31 ℃ (high temperature), and the effects of drought stress on the photosynthetic parameters, gas exchange indicators, and water use efficiency (WUE) of spring wheat leaves under high-temperature conditions were analyzed. The results were as follows: (1) Drought stress significantly reduced the net photosynthetic rate (Pn) of spring wheat, ranging from 22.8% to 57.1%. The reduction range was greater under high-temperature conditions than under suitable temperature conditions. Moreover, significant photoinhibition was observed under strong light. Drought treatment under high-temperature conditions further reduced the light intensity threshold for spring wheat leaves to reach light saturation. Long-term high temperatures and drought reduced the apparent quantum efficiency, maximum net photosynthetic rate, dark respiration rate, and light saturation point of spring wheat leaves and increased the light compensation point. (2) Drought led to a decrease in the stomatal conductance and transpiration rate, and the intercellular CO2 concentration increased under high light intensity in the T1 treatment. Stomatal restriction was the main issue in the T2 treatment of spring wheat leaves, whereas in the T1 treatment, photosynthetic organ damage occurred at high temperatures, leading to non-stomatal restriction. (3) The overall WUE decreased in the following order: T2 > CK > T1. With increasing light intensity, WUE increased in the CK treatment, increased under suitable temperatures but decreased under high temperatures in the T2 treatment, and showed a trend of first increasing and then decreasing in the T1 treatment. This study provides a theoretical basis for water-saving irrigation and the cultivation of stress-resistant spring wheat in arid areas.