Growth and yield responses of Pakistan rice ( Oryza sativa L.) cultivars to O 3 and NO 2

Abstract

Two separate experiments were undertaken to determine Pakistan rice ( Oryza sativa L.) cultivar responses to air pollution, and specifically to test whether O 3 was the pollutant likely to have caused the large effects of filtration on rice yield found in earlier field experiments in Pakistan. In the first experiment (Exp 1), cv. IRRI-6 was exposed to ozone (O 3) at a mean concentration of 43 nl l −1 (8 h day −1) for 133 days until final harvest, covering both the vegetative and reproductive stages of growth. Results showed a significant reduction in total grain weight per plant. In the second experiment (Exp 2), fumigation of two rice cultivars with O 3 at 40−42 nl l −1 (8 h day −1) and nitrogen dioxide (NO 2) at 21–23 nl l −1 (24 h day −1), both singly and in combination, was carried out for 42 days during the vegetative stage of growth to determine if the presence of low concentrations of NO 2 might influence the responses of both cultivars to O 3. Results showed O 3 to be more phytotoxic than NO 2 at the concentrations used. No significant O 3×NO 2 interactions were found at the time of harvest, but O 3 significantly reduced the photosynthetic capacity and biomass of both cultivars. Results of both experiments are compared with those reported for an open-top chamber filtration experiment carried out in Pakistan using the same two rice cultivars. Grain yield of cv. IRRI-6 was decreased in the closed chamber experiment by 57%, compared to a 37% decrease in the open-top chamber experiment; different yield components were affected in the open-top and closed chamber experiments which may be the result of differences in environmental conditions between the two studies. The results suggest that O 3 may have significant effects on rice yield in Pakistan and indicate that Pakistan rice cultivars have a high sensitivity to O 3.