IN-SITU GAS-EXCHANGE RESPONSES OF BOREAL VEGETATION TO ELEVATED CO2 AND TEMPERATURE - FIRST SEASON RESULTS

The climate change experiment (CLIMEX) uses a large greenhouse to inve stigate the responses of an entire undisturbed boreal forested catchme nt to elevated CO2 (560 ppm) and temperature (+3 degrees C in summer a nd +5 degrees C in winter) treatments. In July and September of the fi rst season of treatment the two dominant tree species, Pinus sylvestri s and Betula pubescens, and the ground shrub Vaccinium myrtillus all s howed an increase in leaf photosynthetic rates relative to the plants growing in the control section of the greenhouse and in an outside ref erence catchment. Stomatal density of needles of II sylvestris, and le aves of B. pubescens and V. myrtillus decreased under CO2 enrichment a nd temperature increases relative to the controls. Gas exchange and st able carbon isotope measurements will be made in future growing season s to investigate whether acclimatory adjustments in plant metabolism o ccur-a critical issue affecting the carbon balance of these ecosystems .