Acidic rain and ozone (O-3) may have serious consequences on the growt
h and development of loblolly pine (Pinus taeda L.), a tree species of
major economic importance in the southeastern United States. In two i
ndependent studies, seedlings of open-pollinated families of loblolly
pine were exposed to five concentrations of O-3 (0, 80, 160, 240, or 3
20 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, se
condary 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 suppres
sed 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. Result
s indicate that acid rain probably has little effect on growth of lobl
olly pine seedlings, but O-3 can suppress growth to varying degrees de
pending on family.