Effects of Low Concentration of Ozone, Singly, and in Combination with Sulphur Dioxide on Net Photosynthesis Rates ofVicia fabaL.

Publisher Website
Google Scholar
Abstract
Net photosynthesis rates (PN) of Viciafaba plants were measured in chambers containing either clean air or air containing between 50 and 300 parts 10−9 ozone (O3) with or without 40 parts 10− 9 SO2. Exposure to O3 concentrations greater than 50 parts 10− 9 for periods of 4 h resulted in reductions in PN with greater reductions at higher concentrations. After exposure ceased, recovery of pre-exposure PN depended on O3 concentration. Exposure to less than 90. 100 parts 10− 9 was followed by complete recovery after 20 h whereas 200-300 parts 10− 9 resulted in visible injury and irreversible depression of PN. The addition of 40 parts 10− 9 SO2 to O3 significantly decreased Ps but the effect of SO2 declined with increasing O3. The addition of SO2 had no significant affect on recovery patterns. It is postulated that Vicia faba plants are able to tolerate the absorption of O, up to a threshold above which progressive decreases in PN occur due to effects on photosynthetic processes. The slow and sometimes incompletely reversible effects of O3 on PN indicate cellular differences in the injury mechanism and repair capacity compared with the action of SO2 alone. Low concentrations of O3 with SO2 result in additive injury to PN suggesting independent action of the pollutants, but the reduction in SO2 action with increasing O3 indicates a limit for potential physiological injury More the onset of visible injury.