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Stomatal uptake of O3 in aspen and aspen-birch forests under free-air CO2 and O3 enrichment |
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| Authors: | Johan Uddling Alan J Hogg Ronald M Teclaw David S Ellsworth |
| Institution: | a Department of Plant and Environmental Sciences, University of Gothenburg, P.O. Box 461, SE-405 30 Göteborg, Sweden b Sweetland Writing Center, University of Michigan, 434 S. State St., Ann Arbor, MI 48109, USA c USDA Forest Service, Northern Research Station, Institute for Applied Ecosystem Studies, Rhinelander, WI 54501, USA d Department of Atmospheric, Oceanic, and Space Sciences, 2455 Hayward, University of Michigan, Ann Arbor, MI 48109, USA e Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA f Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA g Centre for Plant and Food Science, University of Western Sydney, Locked Bag 1797, Penrith South DC NSW 1797, Australia |
| Abstract: | Rising atmospheric carbon dioxide (CO2) may alleviate the toxicological impacts of concurrently rising tropospheric ozone (O3) during the present century if higher CO2 is accompanied by lower stomatal conductance (gs), as assumed by many models. We investigated how elevated concentrations of CO2 and O3, alone and in combination, affected the accumulated stomatal flux of O3 (AFst) by canopies and sun leaves in closed aspen and aspen-birch forests in the free-air CO2-O3 enrichment experiment near Rhinelander, Wisconsin. Stomatal conductance for O3 was derived from sap flux data and AFst was estimated either neglecting or accounting for the potential influence of non-stomatal leaf surface O3 deposition. Leaf-level AFst (AFstl) was not reduced by elevated CO2. Instead, there was a significant CO2 × O3 interaction on AFstl, as a consequence of lower values of gs in control plots and the combination treatment than in the two single-gas treatments. In addition, aspen leaves had higher AFstl than birch leaves, and estimates of AFstl were not very sensitive to non-stomatal leaf surface O3 deposition. Our results suggest that model projections of large CO2-induced reductions in gs alleviating the adverse effect of rising tropospheric O3 may not be reasonable for northern hardwood forests. |
| Keywords: | Carbon dioxide FACE Forest Ozone flux Stomata |
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