Carbon gain and bud physiology in Populus tremuloides and Betula papyrifera grown under long-term exposure to elevated concentrations of CO2 and O3
Johanna Riikonen (1, 2), Karte Kets (3), Joseph Darbah (4), Elina Oksanen (5), Anu Sober (3), Elina Vapaavuori (6), Mark E. Kubiske (7), Neil Nelson (7) and David F. Karnosky (4)
1. Department of Ecology and Environmental Science, University of Kuopio, PO Box 1627, FIN-70211, Kuopio, Finland / 2. Corresponding author () / 3. Institute of Botany and Ecology, University of Tartu, Lai 40, 51005 Tartu, Estonia / 4. School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA / 5. Faculty of Biosciences, University of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland / 6. Finnish Forest Research Institute, Suonenjoki Research Unit, FIN-77600 Suonenjoki, Finland / 7. USDA Forest Service, Forestry Sciences Laboratory, Rhinelander, WI 54501, USA / Received June 26, 2007; accepted August 24, 2007; published online December 3, 2007
Summary
Paper birch (Betula papyrifera Marsh.) and three trembling aspen clones (Populus tremuloides Michx.) were studied to determine if alterations in carbon gain in response to an elevated concentration of CO2 ([CO2]) or O3 ([O3]) or a combination of both affected bud size and carbohydrate composition in autumn, and early leaf development in the following
spring. The trees were measured for gas exchange, leaf size, date of leaf abscission, size and biochemical characteristics
of the overwintering buds and early leaf development during the 8th–9th year of free-air CO2 and O3 exposure at the Aspen FACE site located near Rhinelander, WI. Net photosynthesis was enhanced 49–73% by elevated [CO2], and decreased 13–30% by elevated [O3]. Elevated [CO2] delayed, and elevated [O3] tended to accelerate, leaf abscission in autumn. Elevated [CO2] increased the ratio of monosaccharides to di- and oligosaccharides in aspen buds, which may indicate a lag in cold acclimation.
The total carbon concentration in overwintering buds was unaffected by the treatments, although elevated [O3] decreased the amount of starch by 16% in birch buds, and reduced the size of aspen buds, which may be related to the delayed
leaf development in aspen during the spring. Elevated [CO2] generally ameliorated the effects of elevated [O3]. Our results show that both elevated [CO2] and elevated [O3] have the potential to alter carbon metabolism of overwintering buds. These changes may cause carry-over effects during the
next growing season.
Keywords:
bud burst, bud carbohydrates, bud size, gas exchange, leaf abscission, leaf area index, leaf size, paper birch, phenology,
photosynthesis, trembling aspen.
