The Alleviating Effect of Elevated CO 2 on Heat Stress Susceptibility of Two Wheat ( T riticum aestivum L.) Cultivars

Abstract This study analysed the alleviating effect of elevated CO 2 on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars ( Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l −1 ) and elevated (800 μl l −1 ) CO 2 with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II ( PSII ) photochemistry ( F v / F m ) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced P N and F v / F m in both wheat cultivars, but plants grown in elevated CO 2 maintained higher P N and F v / F m in comparison with plants grown in ambient CO 2 . Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO 2 . The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO 2 and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO 2 . This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.