Scots pines (Pinus sylvestris L.), age 2025 years, were subjected to elevated temperature (T), elevated CO2 and the combination of both factors four years in open-top chambers. The treatments were replicated four times. Farquhar & von Caemmerer's (1982) equations for photosynthesis of C3 plants were parameterized with the aim of determining how elevating T and CO2 could affect photosynthetic performance.
The CO2 treatment increased the maximum RuP2 (ribulose 1,5-bisphosphate) saturated rate of carboxylation, (Vcmax), the light-saturated potential rate of electron transport, (Jmax), but decreased the CO2-compensation point (G*), and the day respiration rate (Rd) at lower temperatures and vice versa at higher temperatures. The T treatment and the combination of T and CO2 reduced Vcmax and Jmax, and enhanced G* and Rd at lower temperatures, and vice versa at higher temperatures. The T treatment and the combination of T and CO2 resulted in an upward shift of 1.5 °C and 0.5 °C, respectively, while the CO2 treatment resulted in a downward shift of 1.3 °C in the optimum temperature for photosynthesis.
The long-term elevation CO2 led to a significant increase in the sensitivity of Gs to VPD, Io (flux density) and Tl (needle temperature). The elevation of T alone, or combined with CO2, had the opposite effect. The CO2 elevation increased water use efficiency (WUE). Given Tl = 20 °C, VPD = 0.6 kPa and Io > 1200 µmol m2 s1, the elevation of CO2 alone, or combined with increasing T, decreased the value of Gs by 20.25% and 19.78%, and increased WUE by 51.32% and 50.00%, respectively. Gs increased by 9.66% and WUE decreased by 6.33%, when only temperature elevation was applied in the long-term treatment.
Key words: photosynthesis, transpiration, acclimation, climate change, Scots pine.
Correspondence: Seppo Kellomäki, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland
Telefax: +358-73-1513590
E-mail: kello@joyl.joensuu.fi