Impact of heat and ozone stress on rice growth and productivity: interactive and mitigating effects.

Rising global temperatures promote the formation of surface ozone (O), increasing the likelihood of simultaneous exposure to high temperature and O stress in crops. Although their individual effects have been studied extensively, the combined effects of heat and O stress on rice remain insufficiently understood. This study investigated the physiological and yield-related responses of rice (Oryza sativa L., cv. Sindongjin) to elevated temperature and O. A temperature-gradient field chamber system was used to assess combined stress responses throughout the entire growing season under natural solar radiation and daylength over two years. Additional growth chamber experiments were conducted to evaluate stage-specific responses under controlled environmental conditions. Under ambient O condition, grain yield decreased by 23.1 % at +1.5 °C and 47.2 % at +3.0 °C. Elevated O alone reduced yield by 8.1 %, but no additional yield loss occurred under combined heat and O stress at +3.0 °C. Interestingly, O exposure appeared to partially mitigate heat-induced yield loss. Heat reduced anthocyanin accumulation and photosynthetic efficiency, whereas ozone enhanced anthocyanin levels and partially restored physiological function under combined conditions. The impact of stress varied across developmental stages, with the greatest yield losses occurring from meiosis to heading. These findings reveal complex interactions between temperature and O stress in rice and suggest that elevated O exposure can induce physiological responses that alleviate heat damage. The identified physiological and molecular responses provide actionable targets for improving rice resilience to concurrent heat and ozone stress, guiding both breeding and cultivation practices for climate adaptation.