Current issue: 56(4)
Grasses Agropyron spicatum Pursh, Lolium perenne L. (S23) and 2-year old Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) were exposed to low SO2 concentrations under field conditions for approximately eleven weeks. SO2 was released continuously via manifold delivery systems, and provided treatment mean concentrations of 0.007 (ambient air), 0.042, 0.106 and 0.198 ppm. The concentrations in each treatment were approximately log-normally distributed, with standard geometric deviations ranging from 2.58 to 3.24. In both grass species, 0.198 ppm SO2 caused substantial reduction of total growth. In L. perenne, this was largely the result of impaired root growth, whereas both shoot and root growth of A. spicatum were reduced. 0.106 ppm SO2 had no significant effect on A. spicatum growth, but reduced root growth of L. perenne. Growth of Douglas fir was reduced in each of the tree highest concentrations, with root growth being markedly diminished, particularly on trees which showed chlorotic and necrotic injury. However, in these trees the shoot and total leaf weights tended to increase at the highest SO2 concentrations, suggesting that in these plants injury to leaves stimulated further shoot growth at the expense of root development.