Canadian Forest Service Publications

Tropospheric O3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project. 2003. Karnosky, D.F.; Zak, D.R.; Pregitzer, K.; 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.J.F.; Percy, K.E.; Podila, G.K.; Riemenschneider, D.E.; Sharma, P.; Thakur, R.; Sôber, A.; Sober, J.; Jones, W.S.; Anttonen, S.; Vapaavuori, E.; Mankovska, B.; Heilman, W.; Isebrands, J.G. Functional Ecology 17: 289-304.

Year: 2003

Issued by: Atlantic Forestry Centre

Catalog ID: 22842

Language: English

Availability: Order paper copy (free), PDF (download)

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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, O3-sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late-successional, O3-tolerant species Sugar Maple, Acer saccharum). 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 O3-tolerant as well as O3-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), O3 offsets or moderates the responses induced by elevated CO2. After 3 years of exposure to 560 mmol 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, O3 at 1.5 x ambient completely offset the growth enhancement by CO2, both for O3-sensitive and O3-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.