Southern Research Station

Title: Effects of Tropospheric O₃ on Trembling Aspen and Interaction with CO₂: Results From An O₃-Gradient and a Face Experiment

Author: Karnosky, D.F.; Mankovska, B.; Percy, K.; Dickson, R.E.; Podila, G.K.; Sober, J.; Noormets, A.; Hendrey, G.; Coleman, Mark D.; Kubiske, M.; Pregitzer, K.S.; Isebrands, J.G.

Date: 1999

Source: Water, Air, and Soil Pollution 116: 311-322, 1999.

Description: Abstract. Over the years, a series of trembling aspen (Populus tremuloides Michx.) clones differing in O₃ sensitivity have been identified from OTC studies. Three clones (216 and 271[(O₃ tolerant] and 259 [O₃ sensitive]) have been characterized for O₃ sensitivity by growth and biomass responses, foliar symptoms, gas exchange, chlorophyll content, epicuticular wax characteristics, and antioxidant production. In this study we compared the responses of these same clones exposed to O₃ under field conditions along a natural O₃ gradient and in a Free-Air CO₂ and O₃ Enrichment (FACE) facility. In addition, we examined how elevated CO₂ affected O₃ symptom development. Visible O₃ symptoms were consistently seen (5 out of 6 years) at two of the three sites along the O₃ gradient and where daily one-hour maximum concentrations were in the range of 96 to 125 ppb. Clonal differences in O₃ sensitivity were consistent with our OTC rankings. Elevated CO₂ (200 ppm over ambient and applied during daylight hours during the growing season) reduced visible foliar symptoms for all three clones from 31 to 96% as determined by symptom development in elevated O₃ versus elevated O₂ + CO₂ treatments. Degradation of the epicuticular wax surface of all three clones was found at the two elevated or gradient sites. This degradation was quantified by a coefficient of occlusion which was a measure of stomatal occlusion by epicuticular waxes. Statistically significant increases in stomatal occlusion compared to controls were found for all three clones and for all treatments including elevated CO₂, elevated 4, and elevated CO₂ + O₃. Our results provide additional evidence that current ambient O₃ levels in the Great Lakes region are causing adverse effects on trembling aspen. Whether or not elevated CO₂ in the future will alleviate some of these adverse effects, as occutred with visible symptoms but not with epicuticular wax degradation, is unknown.

Keywords: ozone, carbon dioxide, FACE, aspen, greenhouse gases, climate change, gradients

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Citation

Karnosky, D.F.; Mankovska, B.; Percy, K.; Dickson, R.E.; Podila, G.K.; Sober, J.; Noormets, A.; Hendrey, G.; Coleman, Mark D.; Kubiske, M.; Pregitzer, K.S.; Isebrands, J.G.  1999.  Effects of Tropospheric O₃ on Trembling Aspen and Interaction with CO₂: Results From An O₃-Gradient and a Face Experiment.   Water, Air, and Soil Pollution 116: 311-322, 1999.