CO₂ EXCHANGE RATES AND STOMATAL DIFFUSIVE RESISTANCE IN SOYBEAN EXPOSED TO O₃ AND SO₂

Effects on Photosynthesis, Carbon Allocation, and Plant Growth Associated With Air Pollutant Stress

“…Ormrod et al (1981) and Black et al (1982) studied the response of broad bean to 0 3 with or without S02 added at a concentration of 0·04 ppm for 4 h. The results suggested a synergistic response to concentrations of 0 3 between approximately 0·06 to 0·15 ppm and an additive or antagonistic response to 0 3 concentrations above that level. Furukawa and Totsuka (1979) observed a synergistic decrease in photosynthesis of sunflower at concentrations of 0·20 ppm each of S02 and 0 3 , Chevone and Yang (1985) observed that either 0·20 ppm 0 3 or 0·70 ppm S02 administered separately for 2 h did not significantly affect photosynthetic rates of soybean, but the combination of the two gases at the same concentrations caused a 70% reduction. With soybean, Le Sueur-Brymer and Ormrod (1984) tested the effects of S02 (0·30 ppm) and 0 3 (0·067 ppm) separately and combined.…”

Direct Effects of Atmospheric Sulfate Deposition on Vegetation

“…The mechanism(s) responsible for the more deleterious effects of pollutant combinations on plant growth are not known, but may involve alterations in photosynthetic electron flow which limit carbon reduction. 19 Simulated acidic precipitation at pH 5.6, 4.3 or 3.0, in itself, had little effect on seedling yellow poplar growth. 16 Lee and Weber 20 reported that, in general, growth of eleven woody species was also unaffected by simulated acid rain.…”