Carryover effects of acid rain and ozone on the physiology of multiple flushes of loblolly pine seedlings

The effects of acid rain and ozone exposure on loblolly pine (Pinus taeda L.) seedlings in the Piedmont of North Carolina were assessed over two exposure seasons (1987-1988). Direct effects and carryover effects of long-term exposure on the photosynthetic potential and photopigment concentrations of different needle age-classes were studied. Three half-sib families were grown in open-top field chambers and exposed to two acid rain treatments (pH 5.3 or 3.3) and five ozone exposures delivered in proportion to ambient concentrations (0.5X to 3.0X ambient) in a complete factorial design. Ozone significantly affected photosynthesis but there were no statistically significant effects of acid rain nor any ozone X acid rain interactions. In 1987, photosynthesis of the 1987 first-flush progressively diverged among the ozone treatments except between charcoal-filtered (CF approximately 0.5X ambient) and nonfiltered air (NF). At the end of the first season, photosynthesis was reduced 24% at 1.5X compared to CF and more than 80% at 2.25X and 3.0X. Chlorophyll and carotenoid concentrations were similarly reduced at elevated ozone exposures. In 1988, photosynthesis of the 1987 first-flush in the elevated ozone treatments remained lower. Early in the second season, the 1988 first-flush had a 25% to 50% lower photosynthetic potential at 2.25X and 3.0X compared to CF. This carryover effect on the photosynthetic potential before significant cumulative exposure was progressively smaller in the later 1988 flushes. In the late season flushes in the highest ozone treatments, photosynthesis was significantly higher than in the lower ozone treatments