Effect of ambient-level gas-phase peroxides on foliar injury, growth, and net photosynthesis in Japanese radish (Raphanus sativus).

To investigate the effects of ambient-level gas-phase peroxides concurrent with O(3) on foliar injury, photosynthesis, and biomass in herbaceous plants, we exposed Japanese radish (Raphanus sativus) to clean air, 50 ppb O(3), 100 ppb O(3), and 2-3 ppb peroxides + 50 ppb O(3) in outdoor chambers. Compared with exposure to 100 ppb O(3), exposure to 2-3 ppb peroxides + 50 ppb O(3) induced greater damage in foliar injury, net photosynthetic rates and biomass; the pattern of foliar injury and the cause of net photosynthetic rate reduction also differed from those occurring with O(3) exposure alone. These results indicate for the first time that sub-ppb peroxides + 50 ppb O(3) can cause more severe damage to plants than 100 ppb O(3), and that not only O(3), but also peroxides, could be contributing to the herbaceous plant damage and forest decline observed in Japan's air-polluted urban and remote mountains areas.