Tropospheric 03 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project
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Functional Ecology 17:289-304
1. The impacts of elevated atmospheric CO2 and/or O3 have been examined over 4 years using an open-air exposure system in an aggrading northern temperate forest containing two different functional groups (the indeterminate, pioneer, 03-sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late successional, 03-tolerant species Sugar Maple, Acer saccharum). 2. The responses to these interacting greenhouse gases have been remarkably consistent in pure Aspen stands and in mixed Aspen/Birch and Aspen/Maple stands, from leaf to ecosystem level, for 03-tolerant as well as 03-sensitive genotypes and across various trophic levels. These two gases act in opposing ways, and even at low concentrations (1?5 x ambient, with ambient averaging 34-36 nL L-1 during the summer daylight hours), 03 offsets or moderates the responses induced by elevated CO2. 3. After 3 years of exposure to 560 ?mol mol-1 CO2, the above-ground volume of Aspen stands was 40% above those grown at ambient CO2, and there was no indication of a diminishing growth trend. In contrast, 03 at 1?5 x ambient completely offset the growth enhancement by CO2, both for 03-sensitive and 03-tolerant clones. Implications of this finding for carbon sequestration, plantations to reduce excess CO2, and global models of forest productivity and climate change are presented.
Karnosky, D. F.; Zak, D. R.; Pregitzer, K. S.; Awmack, C. S.; Bockheim, J. G.; Dickson, R. E.; Hendrey, G. R.; Host, G. E.; King, J. S.; Kopper, B. J.; Kruger, E. L.; Kubiske, M. E.; Lindroth, R. L.; Mattson, W. J.; McDonald, E. P.; Noormets, A.; Oksanen, E.; Parsons, W. F. J.; Percy, K. E.; Podila, G. K.; Riemenschneider, D. E.; Sharma, P.; Thakur, R.; Sôber, A.; Sôber, J.; Jones, W. S.; Anttonen, S.; Vapaavuori, E.; Mankovska, B.; Heilman, W.; Isebrands, J. G. 2003. Tropospheric 03 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project. Functional Ecology 17:289-304