Sensitivity of Red Maple Cultivars to Acute and Chronic Exposures of Ozone

Abstract

Five red maple (Acer rubrum) cultivars, 'Autumn Flame', 'Fairview Flame', 'Franksred' (Red Sunset™), 'Northfire' and 'October Glory', and 1 Freeman maple cultivar (Acer°° freemanii 'Autumn Blaze', an interspecific cross between red maple and silver maple) were exposed to 0,100, 200, or 300 ppb ozone for 4 hours on 2 consecutive days. Visible foliar injury, characterized as a stipple on the upper leaf surface, was observed in all ozone treatments except the control, and occurred on the oldest leaves only. 'Autumn Flame' had the least visible injury (less than 1% of the leaves injured), while 'Northfire' had the most (4% of the leaves injured). In a chronic ozone exposure experiment, 3 red maple cultivars ('Autumn Flame', 'Fairview Flame', and 'October Glory'), and 1 Freeman maple cultivar ('Autumn Blaze') were exposed to sub-ambient, ambient, or twice-ambient ozone levels for 9 weeks. No visible foliar injury developed in any of the ozone treatments. No differences for plants in the 3 ozone treatments occurred for height, caliper, leaf, shoot, or root dry weight. Photosynthesis was lower for sub-ambient plants and similar for twice-ambient and ambient plants 4 weeks after treatment initiation, while at 8 weeks no differences occurred. These data indicate that red maple cultivars are relatively tolerant to elevated acute and chronic ozone exposures.