Effect of exogenous ascorbic acid on photosynthesis and growth of rice under O₃ stress

To clarify the effect of changing troposphere ozone (O₃) concentration on rice growth and inhibiting effect of exogenous ascorbic, the effect of exogenous ascorbic acid (ExAsA) on rice photosynthesis and growth under O₃ stress was investigated using open-top chamber (OTC) in rice field. Analysis shows that photosynthetic pigment contents, gas exchange parameters, net assimilation rate (NAR), relative growth rate (RGR), and grain/leaf area ratio of rice notably decrease under O₃ stress. Chlorophyll a (chl a) level, chl a/chl b ratio, photosynthetic rate (Pn), and transpiration rate (Tr) significantly increase, whereas chl b and stomatal conductance (Gs) have no obvious change after ExAsA application. The effect of ExAsA on NAR, RGA, and grain/leaf area ratio is notable under O₃ stress, and is especially remarkable for grain/leaf area ratio. This demonstrates beneficial effect on coordinated development of source and sink, which forms the basis for improving rice yield and quality.