Responses of loblolly pine to ozone and simulated acidic rain

Acidic rain and ozone (O-3) may have serious consequences on the growth and development of loblolly pine (Pinus taeda L.), a tree species of major economic importance in the southeastern United States. In two independent studies, seedlings of open-pollinated families of loblolly pine were exposed to five concentrations of O-3 (0, 80, 160, 240, or 320 nL . L(-1)) and three simulated rain acidities (pH 5.3, 4.3, or 3.3). Following 23 weeks of growth (12 weeks in charcoal-filtered air and 11 weeks of O-3 and simulated acidic rain exposures), stem height, secondary needle dry weight, top and total seedling dry weight, and root/shoot dry weight ratio all were related negatively and linearly with O-3 concentration. Stem diameter and root dry weight were also suppressed by O-3. Suppression of the growth parameters ranged from 14 to 35% for the greatest O-3 concentration. Acidity of simulated rain did not affect seedlings, nor did it affect seedling responses to O-3. Results indicate that acid rain probably has little effect on growth of loblolly pine seedlings, but O-3 can suppress growth to varying degrees depending on family.