ACCLIMATION OF PHOTOSYNTHETIC PARAMETERS IN SCOTS PINE AFTER 3 YEARS EXPOSURE TO ELEVATED-TEMPERATURE AND CO2

Single Scots pine (Pinus sylvestris L.) was subjected to elevated temp erature (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 fie ld measurements of gas exchange, Farquhar and von Caemmerer's basic eq uations for photosynthesis of C-3 plants were parameterized. The value s of the estimated parameters at five ranges of leaf-temperature for t rees growing in four different environments are presented and discusse d. The estimates of the parameters show that Scots pine grown at eleva ted CO2 or elevated temperature, compared to those grown in the ambien t conditions, did not show significant decreases in the maximum RuP2 ( ribulose-1,5-bisphosphate) saturated rate of carboxylation, V-cmax, th e maximum rate of electron transport, J(max) and the 'day respiration rate', R(d), within a given range of measuring temperatures (5-25 degr ees C). But at high measuring temperature (> 30 degrees C), the elevat ed CO2 treatment significantly decreased V(cmax) and J(max) whereas th e elevated temperature or the combination of CO2 and temperature signi ficantly 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 CO 2 and temperature led a slight rightward drift of the curves. The mode l computations show that given a constant intercellular CO2 concentrat ion, C-i (230 or 540 mu mol mol(-1)), there are no significant differe nces in the maximum rates of assimilation among treatments; when C-i w as doubled, the maximum rate of assimilation increased by 28%-34% with no significant differences among treatments.