White ash seedling growth response to ozone and simulated acid rain

Abstract

Five-week-old white ash (Fraxinusamericana L.) were exposed to O3 (0.00, 0.05, 0.10, or 0.15 ppm, 4 h/d, 5 d/week) in combination with simulated rain (pH 3.0, 4.3, or 5.6, 1 h/d, 2 d/week, at 0.75 cm/h) for 5 weeks, under controlled environmental conditions, with rain applied either just before or after fumigation. Across all other treatments, increasing concentrations of O3 resulted in significant linear decreases in root, leaf, and total dry weights, total height increase, root/shoot ratio, and mean relative growth rates of the total plant, stem, root and leaves ([Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], respectively). Significant linear decreases in root dry weight, [Formula: see text], and root/shoot ratio occurred with increasing rain acidity. A significant quadratic response was observed with rain pH for all aboveground variables measured. Growth was the greatest for seedlings treated with pH 4.3 and the least for those treated with pH 5.6 or 3.0 simulated rain. The timing of rain application relative to O3 exposure did not significantly alter any growth variable. Visible symptoms of O3 (0.15 ppm), simulated rain (pH 3.0), or O3 plus simulated rain (0.15 ppm and pH 3.0) were observed on 61, 61, and 54% of the seedlings in each treatment, respectively. The combined effect of O3 and simulated rain resulted in significantly less root dry weight, [Formula: see text], and root/shoot ratio at 0.05 ppm O3 and significantly less [Formula: see text] and root/shoot ratio at 0.10 ppm O3 as rain pH decreased. These findings are discussed relative to the implications of O3 and acidic precipitation on white ash growth.