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 1(-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 1(-1) (8 h day(-1)) and nitrogen dioxide (NO2) at 21-23 nl 1(-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 NO2 might influence the responses of both cultivars to O-3 Results showed O-3 to be more phytotoxic than NO2 at the concentrations used. No significant O3XNO2 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. (C) 1998 Elsevier Science Ltd. All rights reserved. References: 29
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