Both Short-term and Long-term Ozone Pollution Alters the Chemical Composition of rice Grain

The increasing ground-level ozone (O₃) is threatening food security, especially in Asian areas, where rice is one of the most important staple crops. O₃ impacts on rice could be exacerbated by its spatiotemporal heterogeneity. To improve evaluation accuracy and develop effective adaptations, direct data is urgently needed. Studies on the short-term effects of O₃ on rice grain, however, are lacking. Which may lead to an underestimation of the O₃ impacts. Through a field experiment, we studied the responses of grain nitrogen, grain carbon, and grain protein in rice cultivars to elevated concentrations of O₃ (40 ppb plus that in background air, eO₃), especially examining the effects of short-term eO₃ during different plant growth stages. We found that long-term eO₃ increased grain nitrogen by 29.29% in a sensitive rice cultivar, and short-term eO₃ at the tillering and jointing stages increased grain nitrogen by 19.31%, and the grain carbon to nitrogen ratio was decreased by 14.70%, and 21.14% by short-term and long-term eO₃. Here we demonstrate that short-term eO₃ may significantly affect the chemical composition of rice grains. Previous evaluations of the effects of eO₃ may be underestimated. Moreover, changes in the grain nitrogen and grain protein were greater when the short-term eO₃ was added to rice plants during the tillering and jointing stage, compared to heading and ripening stage. These results suggest that to improve the tolerance of rice to eO₃ to achieve food security, studies on cultivar screening, as well as developing growth-stage-specific adaptations are needed in future.