Analysis of drought stress effect on wheat in interaction with high temperatures

The production of wheat is greatly threatened by the global increase in heat and drought stress. The individual effects of these two stressors on different growth and yield traits of wheat have been studied, but the response of wheat to a combination of heat and drought stress cannot be directly extrapolated from the response to each stress factor alone. Previous research has shown that there is a lack of information regarding: <br /> 1. Response of wheat to a combination of heat and drought stress <br /> 2. Interactions between heating method, soil substrate and temperature measurement point, and heat stress under climate change, <br /> 3. Effects of heat and drought interactions before anthesis on grain filling rate and duration. <br /> Three experiments were carried out to improve the understanding on the aforementioned knowledge gaps: <br /> 1. An experiment was conducted to understand how wheat yield and component yield responded to high temperature, drought stress and combined heat and drought. The reproductive stage of development in wheat proved to be the most sensitive stage, and the effects of combined heat and drought on the physiological and yield traits were considerably stronger than those of the individual stress factors alone. However, the magnitude of the effects varied for specific growth- and yield-related traits. In addition, cultivar responses were similar for the heat but different for the drought and combined heat and drought treatments. Generally, heat stress as imposed in this study was less detrimental than the effect of drought and of heat and drought combined. <br /> 2. Three different sites studies were set up to improve the understanding of the reasons for the above findings by testing the response of wheat yield and yield components to differences in heating method, temperature measurement points and soil substrate under sole heat and combined heat and drought stress around anthesis. Grain yield was significantly reduced by heat stress in plants grown on a sandy soil substrate but not in those grown on a soil with a high soil water holding capacity with two heating systems (climate chamber and infrared heaters). Combined heat and drought had a stronger detrimental effect on yield than heat stress alone. Grain number was significantly reduced in all experiments by heat stress and combined heat and drought stress at anthesis. Single grain weight was increased by heat stress around anthesis, and partly compensated lower grain numbers in pots containing soil with a high soil water holding capacity but not in experiments with a sandy soil substrate. <br /> 3. A further experiment was conducted to study the impact of heat and drought stress at anthesis on grain filling rate, grain filling duration, photosynthesis rate, chlorophyll content, yield and yield components of three wheat cultivars. The reduction of grain filling duration was fully compensated by increased grain filling rates, so that single grain weights were not significantly different (2 cultivars) or even higher for the heat treatment (1 cultivar) under heat stress. In addition, heat and drought stress at anthesis reduced the grain number and grain yield. Drought stress accelerated earlier flag leaf senescence and reduced photosynthesis rates during grain filling but not in the plants exposed to heat. This indicates that source limitations may explain the differences in grain filling rates between the treatments. The results demonstrate that the impact of stress at anthesis on the subsequent grain filling period differs between heat and drought stress. Based on the above findings, several conclusions can be drawn. More consideration should be given to the individual and combined impacts of heat and drought stressors on wheat productivity and in crop models. The crop models must also consider the difference in crop response to heat and drought stress during anthesis in various phonological phases. Finally, it is necessary to place more emphasis on substrate soil properties, temperature measurement point and heat imposing procedure.