Influence of two growing seasons of experimental ozone fumigation on photosynthetic characteristics of white oak seedlings.

White oak (Quercus alba L.) seedlings were exposed to charcoal-filtered air or to above-ambient ozone concentrations for 19-20 weeks during each of two growing seasons in continuously stirred tank reactors in greenhouses. Ozone treatments were 0.15 ppm (300 microg m(-3)) for 8 h day(-1), 3 days week(-1) in 1988, and continuous 15% above ambient in 1989. The seedlings were grown in forest soil watered twice weekly with simulated rain of pH 5.2. Responses of net photosynthesis to photosynthetically active radiation and intercellular CO(2) concentration were measured three times each year. There were no significant differences in light-saturated net photosynthesis or stomatal conductance, dark respiration, quantum or carboxylation efficiencies, and light or CO(2) compensation points on any date between control and ozone-exposed seedlings.