Effects of Chronic Doses of Ozone on Loblolly Pine: Photosynthetic Characteristics in the Third Growing Season
Gas exchange characteristics of loblolly pine seedlings were measured in the third growing season of ozone fumigations to determine the effects of long-term ozone exposure on photosynthetic capacity. Light and CO2 response curves indicated significant decreases of 21% and 27%, respectively, in light-saturated and CO2-saturated photosynthetic capacities at 2 x ambient ozone (92 ppb 12-hr seasonal mean) compared to charcoal-faltered (CF) air, approximately 0.5 x ambient ozone (29 ppb 12-hr seasonal mean). Differences in the response curves suggest changes in light-harvesting and biochemical efficiencies as well as changes in the activity of RuBP Carboxylase and the regeneration rate of RuBP. Chlorophyll and carotenoid conditions per unit leaf area were decreased at the high ozone treatment in older flushes. Stomatal resistance limited photosynthesis by about 29% in both CF and 2 x ambient ozone treated plants, suggesting that chronic ozone exposure did not affect stomatal control in loblolly pine. For. Sci. 35(3):745-755.
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