Abstract
Effects of SO2 and soil acidification, alone and in combination, on growth and nutrient status of masson pine seedlings (Pinus massoniana Lamb.) were investigated. Before transplanting the seedlings, the pH of red-yellow soil was adjusted to pH 3.7 or 4.5 by adding a solution of H2SO4. The seedlings were transplanted in the treated soil, then were grown for 18 weeks from 6 June to 10 October, 1993 in open-top chambers (OTC) located in an experimental field (Fuchu, Tokyo). During the growth period, the seedlings were exposed to charcoal-filtered air or SO2 at 50 or 100 ppb (nl/l) in the OTC for 8 h a day (9: 00-17: 00), 5days a week, for 17 weeks from 13 June, 1993.
Yellowish and whitish visible injuries were observed on the needles of the seedlings grown in the soil adjusted to pH 3.7 and exposed to SO2 at 100 ppb. The exposure to SO2 or soil acidification reduced the dry weight growth of the seedlings. However, there were no significant interactive effects of SO2 and soil acidification on the dry weight growth of the seedlings. Although the exposure to SO2 did not change the nutrient status of the seedlings, the concentration of Al or Mn increased, but that of Ca in the shoot reduced in the seedlings grown in the soil adjusted to pH 3.7.
From the results obtained in the present study, forest declines of masson pine observed in China may be closely related to relatively high concentrations of atmospheric SO2, such as above 100 ppb in daily average value, and low soil pH below 4.0 induced by wet or dry deposition of acid substances.
