Acclimation of photosynthetic parameters in Scots pine after three years exposure to elevated temperature and CO2

Single Scots pine (Pinus sylvestris L.) was subjected to elevated temperature (year-round elevation), elevated CO2 (elevation from April 15 to September 15) and a combination of elevated temperature and CO2 for three years in open-topped chambers. Using the data obtained from field measurements of gas exchange, Farquhar and von Caemmerer's basic equations for photosynthesis of C-3 plants were parameterized. The values of the estimated parameters at five ranges of leaf-temperature for trees growing in four different environments are presented and discussed. The estimates of the parameters show that Scots pine grown at elevated CO2 or elevated temperature, compared to those grown in the ambient conditions, did not show significant decreases in the maximum RuP2 (ribulose-1,5-bisphosphate) saturated rate of carboxylation, V-cmax, the maximum rate of electron transport, J(max) and the 'day respiration rate', R(d), within a given range of measuring temperatures (5-25 degrees C). But at high measuring temperature (> 30 degrees C), the elevated CO2 treatment significantly decreased V(cmax) and J(max) whereas the elevated temperature or the combination of CO2 and temperature significantly increased V-cmax and J(max). Furthermore, elevated CO, led to a slight leftward drift of the whole temperature-response curves for V-cmax and J(max); while elevated temperature or the combination of CO2 and temperature led a slight rightward drift of the curves. The model computations show that given a constant intercellular CO2 concentration, C-i (230 or 540 mu mol mol(-1)), there are no significant differences in the maximum rates of assimilation among treatments; when C-i was doubled, the maximum rate of assimilation increased by 28%-34% with no significant differences among treatments.