Responses of loblolly pine to ozone and simulated acidic rain

Abstract

Acidic rain and ozone (O 3 ) may have serious consequences on the growth and development of loblolly pine (Pinustaeda 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.