Cultivar-specific regulation of antioxidant enzyme activity and stomatal closure confer tolerance of wheat to elevated ozone: A two-year open-field study with five cultivars

Elevated concentrations of tropospheric ozone (O3) pose a significant threat to food production in many regions of the world. We conducted a two-year experiment with five winter wheat (Triticum aestivum L.) cultivars, Yangmai16 (Y16), Yangmai23 (Y23), Zhenmai12 (Z12), Yangmai29 (Y29), and Yangmai30 (Y30), to assess photosynthetic traits, lipid peroxidation, and antioxidant systems under ambient (A-O3) or elevated (E-O3; 1.5 times A-O3) O3 in a Free-Air O3-Concentration Enrichment system (FACE). E-O3 accelerated leaf senescence, manifested by marked reductions in photosynthetic rate, stomatal conductance, total antioxidant capacity, and photosynthetic pigment content, accompanied by altered antioxidant enzyme activity and a significant increase in malondialdehyde content (an indicator of lipid peroxidation). Most parameters showed significant inter-cultivar differences, as well as interactions between O3 and cultivar. The response of the antioxidant system in wheat flag leaves was influenced by O3 exposure levels. The response of antioxidant enzymes at the grain filling stage and the timely closure of stomata conferred tolerance to O3. This tolerance was associated with higher antioxidant enzyme activity at the anthesis stage but was not related to the size of stomata. This study provides a crucial theoretical foundation for further breeding O3-tolerant cultivars.