Ozone Suppression of White Pine Net Photosynthesis

Reduction in rates of net photosynthesis following exposure to ozone was observed in eastern white pine saplings prior to the development of visible injury. Branches exposed to consecutive doses of 50–80 pphm ozone for 4 hr and 80–90 pphm ozone for 3 hr appeared to have suppressed net photosynthetic rates but results were confounded by diurnal rate variation. Photosynthetic rates of treated branches returned to normal levels following this initial ozone exposure. A second ozonation involving dosages of 90–100 pphm for 5 and 3 hr was sufficient to reduce rates of net photosynthesis by approximately 80 percent.