title: Leaf photosynthetic characteristics of silver birch during three years of exposure to elevated concentrations of CO2 and O3 in the field.
abstract: Effects of elevated concentrations of carbon dioxide ([CO2]) and ozone ([O3]) on photosynthesis and related biochemistry of two European silver birch (Betula pendula Roth) clones were studied under field conditions during 1999-2001. Seven-year-old trees of Clones 4 and 80 were exposed for 3 years to the following treatments in an open-top chamber experiment: outside control (OC), chamber control (CC), 2x ambient [CO2] (EC), 2x ambient [O3] (EO) and 2x ambient [CO2] + 2x ambient [O3] (EC+EO). During the experiment, gas exchange, chlorophyll fluorescence, amount and activity of Rubisco, concentrations of chlorophyll, soluble protein, soluble sugars, starch, nitrogen (N) and carbon:nitrogen (C:N) ratio were determined in short- and long-shoot leaves. Elevated [CO2] increased photosynthetic rate by around 30% when measurements were made at the growth [CO2]. When measured at ambient [CO2], photosynthesis was around 15% lower in EC trees than in CC trees. This was related to a approximately 10% decrease in total leaf N, to 26 and 20% decreases in the amount and activity of Rubisco, respectively, and to a 49% increase in starch concentration in elevated [CO2]. Elevated [O3] had no significant effect on gas exchange parameters and its effect on biochemistry was small in both clones. However, elevated [O3] decreased the proportion of Rubisco in total soluble proteins and the apparent quantum yield of photosystem II (PSII) photochemistry in light and increased non-photochemical quenching in 2000. The interactive effect of CO2 and O3 was variable. Elevated [O3] decreased chlorophyll concentration only in EO trees, and the EC+EO treatment decreased the total activity of Rubisco and increased the C:N ratio more than the EO treatment alone. The small effect of elevated [O3] on photosynthesis indicates that these young silver birches were fairly tolerant to annual [O3] exposures that were 2-3 times higher than the AOT40 value of 10 ppm.h. set as a critical dose for forest trees.
authors.affiliation: Department of Ecology and Environmental Science, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Riikonen
authors.forename: Toini
authors.initials: T
authors.lastname: Holopainen
authors.forename: Elina
authors.initials: E
authors.lastname: Oksanen
authors.forename: Elina
authors.initials: E
authors.lastname: Vapaavuori
mesh_terms: D000064:Acclimatization / Q000502:physiology; D029662:Betula / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010126:Ozone / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D012621:Seasons; D013213:Starch / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll; D002245:Carbon Dioxide; D010126:Ozone; D013213:Starch; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen