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PROCEEDINGS: Index of Abstracts

OZONE-INDUCED ACCELERATED FOLIAR SENESCENCE: IMPLICATIONS FOR TOXICITY AND COMPENSATION

1-Steimer Professor of Agricultural Sciences, Department of Plant Pathology and Environmental Resources Institute, The Pennsylvania State University, University Park, PA 16802. 2-Graduate Student in Plant Physiology, and Research Assistant in Plant Pathology, respectively, The Pennsylvania State University, University Park, PA 16802.

Two-year-old seedlings of black cherry, Prunus serotina Ehrh., Northern red oak, Quercus rubra L. and sugar maple, Acer saccharum Marsh., and ramets of hybrid poplar, Populus maximowizii x trichocarpa, clone 245 were grown in eight charcoal-filtered open-top chambers per species. Half the chambers, per species, received 0.08 FL L-1 O3 from 1000 to 1800 h each day of the growing season. Accelerated foliar senescence and associated O3-induced loss in Rubisco were observed in older foliage of hybrid poplar and black cherry. Younger leaves were less responsive to O3, and in the case of hybrid poplar actually exhibited signs of compensation to the stress. Sugar maple and northern red oak were less responsive and exhibited no signs of accelerated senescence. The relevance of the latter response is considered in the context of the indeterminate and determinate growth habits of these two groups of plant species.