Effects of elevated ozone concentrations on Thai Jasmine rice cultivars (Oryza sativa L.)

This study investigated the effects of O-3 on growth, yields and physiological characteristics of Thai Jasmine rice cultivars. Rice was exposed to O-3 for 7 h day(-1) in a closed chamber for 113 days, beginning from seedling until harvest. O-3 concentration in each chambers was controlled at 0 ppb, 50 ppb, 100 ppb, 150 ppb and at the ambient level. Effects of O-3 on leaf area index (LAI) became obvious at maturity when LAI significantly decreased in the treatments under elevated O-3 concentrations. Results in shoot biomass indicated that shoot length was more affected by O-3 than shoot dry weight. Root length rather than dry weight was significantly reduced in all cultivars. The most severe damage of O-3 was found in photosynthetic components, namely chlorophyll and carotenoid contents, and rate of net photosynthesis. Yield components were also strongly affected by O-3. The highest reduction in filled seed per ear was found in the Pathumthani 1 cultivar by 78% when it was exposed to 150 ppb O-3 compared to the control (0 ppb). Similarly, 100-grain weight was also reduced as much as 12.3% in this cultivar.