Leaf Biochemical and Physiological Responses to Elevated Atmospheric Ozone Concentration in Eight Modern Rice Cultivars

Abstract

This study investigated the effects of elevated O 3 level on photosynthetic traits and antioxidant systems of various rice genotypes under fully open-air conditions. Eight modern rice cultivars ( Oryza sativa L.), including 4 hybrids and 4 inbreds, were exposed to 2 O 3 treatments: the ambient atmosphere (A-O 3 ) and the 1.5 times ambient O 3 concentration (E-O 3 ) throughout the reproductive period. The measurements of gas exchange, chlorophyll a fluorescence, photosynthetic pigments, lipid oxidation, antioxidant content, and antioxidant enzyme activity were conducted on the flag leaf during the early and late grain-filling periods. The results indicated that E-O 3 had differential effects on the photosynthesis and antioxidant indicators of rice genotypes. In the hybrid rice, the reduction in the light-saturated photosynthetic rate ( A sat ) was primarily due to the nonstomatal factors, such as the changes in antioxidants, particularly ascorbate and carotenoids. In contrast, the reduction in A sat levels in inbred rice was mainly due to the stomatal factors. Additionally, the hybrid rice was more sensitive to O 3 than the inbred rice, with the sensitivity determinants varying between types. The sensitivity of hybrid rice to O 3 was influenced by the magnitude of its antioxidant capacity, whereas the inbred rice sensitivity was determined by the stomatal conductance ( g s ) and the antioxidant enzyme activity. The rice cultivars with higher antioxidant enzyme activities could help mitigate the damage caused by O 3 pollution. This study could provide valuable insights for screening the O 3 -tolerant rice cultivars and promoting the food security sustainability.