Parametrization of a biochemical CO2 exchange model for birch (Betula pendula Roth.)

Gas exchange of one-year-old silver birch (Betula pendula Roth.) seedlings of boreal habitat was studied in laboratory conditions. Seedlings were exposed to stepwise changes in CO2 concentration and irradiance in five constant temperatures ranging from 9 to 33 °C. The Farquhar biochemical model was fitted to the response curves. Values for the photosynthesis parameters Jmax and Vc(max) as well as their temperature dependences were derived from the measurements. Following characteristics of the boreal growth conditions, the response curves were determined also at temperatures below 20 °C. This was, indeed, reflected to photosynthesis parameters, though results showed relatively large variation due to differences among leaves. The gas exchange rates of separate leaves could vary by 40% and also the temperature dependences were slightly different. The slope and curvature of the light response curve were relatively constant above 19 °C and decreased at low temperatures.