EFFECTS OF LOW CONCENTRATIONS OF SULFUR-DIOXIDE ON THE GROWTH OF 4 BROADLEAVED TREE SPECIES

Seedlings of Betula pendula, B. pubescens and Acer pseudoplatanus were exposed to 150 μg m-3 SO2 in chambers for 15-24 weeks during the summer of 1974. In addition, A. pseudoplatanus and Quercus robur were exposed to 170 μg m-3 SO2 for 71 weeks in 1975-76 and B. pendula for 14 weeks in 1975. Exposure to SO2 had no significant effect on stem or root dry weight in any of the experiments. The leaf area ratio and specific leaf area of B. pubescens were significantly reduced by SO2. Leaf area and leaf weight of A. pseudoplatanus were reduced by SO2 in 1974, but there were no significant effects on leaf production in 1975 or 1976. SO2 had no effect on leaf growth in B. pendula or Q. robur. SO2 stimulated height increment in A. pseudoplatanus and Q. robur, but only in the second year of exposure. There was no significant effect of SO2 on height increment in either of the Betula species. Senescence of Q. robur leaves was advanced by 12 days in 1975 and 9 days in 1976, as a result of exposure to SO2 but there was no effect on the time of senescence of A pseudoplatanus leaves in 1975. The sulphur content of leaves was increased by SO2 in all species. The mean date of leaf fall in Q. robur was negatively correlated with the sulphur content of leaves in 1975, but not in 1976. It is concluded that the broadleaved species studied are more tolerant of prolonged exposure to SO2 than is Pinus sylvestris.