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PROCEEDINGS: Index of Abstracts

EFFECTS OF OZONE AND CO2 ON THE GROWTH AND PHYSIOLOGY OF ASPEN

1-Michigan Technological University, School of Forestry and Wood Products, Houghton, MI 49931. 2-University of Minnesota, Duluth, MN. 3-North Central Forest Experiment Station, Forestry Sciences Laboratory, Rhinelander, WI 54501. 4-Estonia Academy of Science, Institute of Ecology/Marine Research, Tartu, Estonia.

During the past three years, we have examined the effects of ozone (O3) and carbon dioxide (CO2), alone and in combination, on the growth and physiology of trembling aspen (Populus tremuloides Michx.). We have conducted several single growing season exposures of potted plants and a three growing season exposure with trees planted in the ground. All studies have been conducted in open-top chambers. Our research demonstrated that aspen is highly sensitive to ozone and that there are strong genotypic differences in response to ozone. Seasonal exposures of 70 to 100 ppm-h have a significant negative impact on height, diameter, leaf and branch retention, and above ground biomass. The O3 sensitivity appears stable as aspen trees reach flowering age. CO2 administered at 150 ppm above background levels did not compensate for the adverse ozone effects. Photosynthesis measurements over all growing seasons and with multiple genotypes suggest that CO2 may increase the O3 sensitivity of otherwise tolerant aspen clones. We are currently developing an unchambered O3 exposure system to more closely simulate forest conditions.