title: Silver birch and climate change: variable growth and carbon allocation responses to elevated concentrations of carbon dioxide and ozone.
abstract: We studied the effects of elevated concentrations of carbon dioxide ([CO2]) and ozone ([O3]) on growth, biomass allocation and leaf area of field-grown O3-tolerant (Clone 4) and O3-sensitive clones (Clone 80) of European silver birch (Betula pendula Roth) trees during 1999-2001. Seven-year-old trees of Clones 4 and 80 growing outside in open-top chambers were exposed for 3 years to the following treatments: outside control (OC); chamber control (CC); 2 x ambient [CO2] (EC); 2 x ambient [O3] (EO); and 2 x ambient [CO2] + 2 x ambient [O3] (EC+EO). When the results for the two clones were analyzed together, elevated [CO2] increased tree growth and biomass, but had no effect on biomass allocation. Total leaf area increased and leaf abscission was delayed in response to elevated [CO2]. Elevated [O3] decreased dry mass of roots and branches and mean leaf size and induced earlier leaf abscission in the autumn; otherwise, the effects of elevated [O3] were small across the clones. However, there were significant interactions between elevated [CO2] and elevated [O3]. When results for the clones were analyzed separately, stem diameter, volume growth and total biomass of Clone 80 were increased by elevated [CO2] and the stimulatory effects of elevated [CO2] on stem volume growth and total leaf area increased during the 3-year study. Clone 80 was unaffected by elevated [O3]. In Clone 4, elevated [O3] decreased root and branch biomass by 38 and 29%, respectively, whereas this clone showed few responses to elevated [CO2]. Elevated [CO2] significantly increased total leaf area in Clone 80 only, which may partly explain the smaller growth responses to elevated [CO2] of Clone 4 compared with Clone 80. Although we observed responses to elevated [O3], the responses to the EC+EO and EC treatments were similar, indicating that the trees only responded to elevated [O3] under ambient [CO2] conditions, perhaps reflecting a greater quantity of carbohydrates available for detoxification and repair in elevated [CO2].
authors.affiliation: Department of Ecology and Environmental Science, University of Kuopio, PO Box 1627, 70211 Kuopio, Finland.
authors.forename: Johanna
authors.initials: J
authors.lastname: Riikonen
authors.forename: Minna-Mari
authors.initials: MM
authors.lastname: Lindsberg
authors.forename: Toini
authors.initials: T
authors.lastname: Holopainen
authors.forename: Elina
authors.initials: E
authors.lastname: Oksanen
authors.forename: Juha
authors.initials: J
authors.lastname: Lappi
authors.forename: Petri
authors.initials: P
authors.lastname: Peltonen
authors.forename: Elina
authors.initials: E
authors.lastname: Vapaavuori
mesh_terms: D029662:Betula / Q000254:growth & development / Q000502:physiology*; D018533:Biomass; D002245:Carbon Dioxide; D017752:Greenhouse Effect; D010126:Ozone; D018515:Plant Leaves / Q000502:physiology; D018547:Plant Stems / Q000254:growth & development; D014197:Trees / Q000254:growth & development / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D010126:Ozone