Effects of air pollutants on apparent photosynthesis and water use by citrus trees.

H Commercially producing lemon and navel orange trees were tested t o determine the effects of ambient air pollutants which occur in the Los Angeles basin on water use (transpiration) and apparent photosynthesis. The entire trees were enclosed in plastic covered greenhouses and were supplied various fractions of the atmosphere to find out whether ozone, peroxyacyl nitrates, or fluorides were causing deleterious effects. Nitric oxide was added t o the air in one treatment to reduce ozone selectively but in so doing, nitrogen dioxide in amounts equal to the ozone was formed. The results showed that the total photochemical smog complex reduced the rate of water use by lemon trees and also reduced the rate of apparent photosynthesis. Fluoride levels occurring in the atmosphere caused no detectable effects. Attempts to evaluate the separate effects of ozone and peroxyacyl nitrates were unsuccessful. Reduction of the ozone in the tree atmospheres by addition of nitric oxide failed t o overcome the reduced water use and lowered apparent photosynthesis.