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 investigate the responses of an entire undisturbed boreal forested catchment to elevated CO2 (560 ppm) and temperature (+3 degrees C in summer and +5 degrees C in winter) treatments. In July and September of the first season of treatment the two dominant tree species, Pinus sylvestris and Betula pubescens, and the ground shrub Vaccinium myrtillus all showed an increase in leaf photosynthetic rates relative to the plants growing in the control section of the greenhouse and in an outside reference catchment. Stomatal density of needles of II sylvestris, and leaves of B. pubescens and V. myrtillus decreased under CO2 enrichment and temperature increases relative to the controls. Gas exchange and stable carbon isotope measurements will be made in future growing seasons to investigate whether acclimatory adjustments in plant metabolism occur-a critical issue affecting the carbon balance of these ecosystems.