title: Respiratory responses of Scots pine stems to 5 years of exposure to elevated CO2 concentration and temperature.
abstract: Stem respiration in 20-year-old Scots pine (Pinus sylvestris L.) trees was examined following 5 years of exposure to ambient conditions (CON), elevated atmospheric carbon dioxide concentration ([CO2]) (ambient + 350 micromol mol(-1), (EC)), elevated temperature (ambient + 2-6 degrees C, (ET)) or a combination of elevated [CO2] and elevated temperature (ECT). Stem respiration varied seasonally regardless of the treatment and displayed a similar trend to temperature, with maximum rates occurring around Day 190 in summer and minimum rates in winter. Respiration normalized to 15 degrees C (R15) was higher in the growing season than in the non-growing season, whereas the temperature coefficient (Q10) was lower in the growing season. Annually averaged R15 was 0.36, 0.43, 0.40 and 0.44 micromol m(-2) s(-1) under CON, EC, ET and ECT conditions, respectively, whereas the corresponding values for total stem respiration were 6.55, 7.69, 7.50 and 7.90 mol m(-2) year(-1). The EC, ET and ECT treatments increased R15 by 18, 11 and 22%, respectively, relative to CON, and increased the modeled annual total stem respiration by 18, 15 and 21%. The increase in modeled annual stem respiration under EC and ECT conditions was caused mainly by higher maintenance respiration (22 and 25%, respectively, whereas the increase in growth respiration was 9 and 12%). Growth respiration was unaltered by ET. The treatments did not significantly affect the respiratory response to stem temperature; the mean Q10 value was 2.04, 2.10, 1.99 and 2.12 in the CON, EC, ET and ECT treatments, respectively. It is suggested that the increase in stem respiration was partly a result of the increased growth rate. We conclude that elevated [CO2] increased the maintenance component of respiration more than the growth component.
authors.affiliation: Faculty of Forestry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland. tianshan.zha@forest.joensuu.fi
authors.forename: Tian-Shan
authors.initials: TS
authors.lastname: Zha
authors.forename: Seppo
authors.initials: S
authors.lastname: Kellomäki
authors.forename: Kai-Yun
authors.initials: KY
authors.lastname: Wang
authors.forename: Aija
authors.initials: A
authors.lastname: Ryyppö
mesh_terms: D002245:Carbon Dioxide; D019069:Cell Respiration / Q000502:physiology; D041605:Pinus sylvestris / Q000378:metabolism / Q000502:physiology*; D018547:Plant Stems / Q000378:metabolism; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000378:metabolism / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide