Acute O3 damage on first year coppice sprouts of aspen and maple sprouts in an open-air experiment

Abstract

We studied the effect of high ozone (O₃) concentration (110–490 nmol mol⁻¹) on regenerating aspen (Populus tremuloides) and maple (Acer saccharum) trees at an open-air O₃ pollution experiment near Rhinelander WI USA. This study is the first of its kind to examine the effects of acute O₃ exposure on aspen and maple sprouts after the parent trees, which were grown under elevated O₃ and/or CO₂ for 12 years, were harvested. Acute O₃ damage was not uniform within the crowns of aspen suckers; it was most severe in the mature, fully expanded photosynthesizing leaves. Young expanding leaves showed no visible signs of acute O₃ damage contrary to expectations. Stomatal conductance played a primary role in the severity of acute O₃ damage as it directly controlled O₃ uptake. Maple sprouts, which had lower stomatal conductance, smaller stomatal aperture, higher stomatal density and larger leaf surface area, were tolerant of acute O₃ exposure. Moreover, elevated CO₂ did not ameliorate the adverse effects of acute O₃ dose on aspen and maple sprouts, in contrast to its ability to counteract the effects of long-term chronic exposure to lower O₃ levels.