Growth Response of Green and White Ash Seedlings to Ozone, Sulfur Dioxide, and Simulated Acid Rain

Abstract

Abstract Nine-week-old green (Fraxinus pennsylvanica Marsh.) and white (F. americana L.) ash were exposed to O3 and/or SO2 (control, 0.10 ppm O3, 0.08 ppm SO2 or 0.10 ppm O3 + 0.08 ppm SO2) for 4 h d-1, 5 d wk-1 in combination with simulated rain (pH 3.0, 4.3 or 5.6, 1 h d-1, 2 d wk-1 at 0.75 cm h-1) for 6 weeks, under controlled laboratory conditions, with rain applied either just before or after fumigation. Across all rain treatments, white ash biomass was suppressed by the application of O3 and cumulative shoot elongation of green ash exposed to O3 and/or SO2 was less than controls. The combination of O3 + SO2 did not affect the growth of either species more than the pollutants applied alone. Leaf area ratio (LAR) and root to shoot ratio (RSR) exhibited quadratic responses to rain pH in green ash, across all pollutant treatments. Significant pollutant x pH interactions occurred in leaf weight ratio (LWR) in green ash and LAR and RSR in white ash. Significant linear increases in LAR and decreases in RSR, with decreasing pH, were observed for O3 and SO2-treated white ash. These findings are discussed relative to implications of the effects of gaseous pollutants in combination with acid rain on green and white ash growth. For. Sci. 34(4):1016-1029.