Effects of SO₂ on Growth of Two Age Classes of Chamaecyparis obtusa Seedlings

Tsukahara, Hatsuo, Kozlowski, Theodore T., and Shanklin, John: Effects of SO₂ on growth of two age classes of Chamaecyparis obtusa seedlings J. Jpn. For. Soc. 68: 349~353, 1986 Chamaecyparis obtusa Sieb. et Zucc. Seedlings of two age classes (109- and 202-days old) were exposed to 0, 0. 5, 1. 0, or 1. 5 μl/l SO₂ for 144 hr. Visible foliar injury was not induced by any SO₂ dosage up to 60 days after treatment, indicating high pollution tolerance of the species. However, seedling growth was inhibited by SO₂, with the amount of growth reduction varying with the SO₂ dosage, age of seedlings, and the parameters used to determine growth response. Both height and stem diameter growth were reduced in the younger seedlings by SO2, but not in the older seedlings. Exposure to SO₂ did not significantly reduce the dry weight increases of seedlings, leaves, or stems of either age class, but reduced root growth in the older seedlings only. The inhibitory effects of SO₂ on growth of both age classes were more apparent when based on relative growth rates than on dry-weight increment of the seedlings and various plant parts.