Age of Pine Seedlings with Primary Needles Affects Sensitivity to Ozone and Sulfur Dioxide

Seedlings of Virginia (Pinus virginiana), shortleaf (P. echinata), slash (P. elliottii var. elliottii), and loblolly (P. taeda) pines at ages 2, 4, 6, 8, and 10 wk were exposed to individual dosages of ozone and sulfur dioxide. Exposures were 2 hr at 655.0 +/- 65 ..mu..g/m/sup 3/ for SO/sub 2/ and 477.5 +/- 48 ..mu../m/sup 3/ for O/sub 3/ (25 +/- 2.5 parts per hundred million). The two gases were equally injurious to all species, and all species were equally sensitive to each gas. Maximum sensitivity of the seedlings to the two gases, however, occurred at different ages. For ozone the greatest sensitivity was 2 wk or younger, and for sulfur dioxide at 8 to 10 wk or older.