IMPACTS OF ELEVATED CARBON-DIOXIDE AND TEMPERATURE ON A BOREAL FORESTECOSYSTEM (CLIMEX PROJECT)

To evaluate the effects of climate change on boreal forest ecosystems, both atmospheric CO2 (to 560 ppmv) and air temperature (by 3 degrees- 5 degrees C above ambient) were increased at a forested headwater catc hment in southern Norway. The entire catchment (860 m(2)) is enclosed within a transparent greenhouse, and the upper 20% of the catchment ar ea is partitioned such that it receives no climate treatment and serve s as an untreated control. Both the control and treatment areas inside the greenhouse receive deacidified rain. Within 3 years, soil nitroge n (N) mineralization has increased and the growing season has been pro longed relative to the control area. This has helped to sustain an inc rease in plant growth relative to the control and has also promoted in creased N export in stream water. Photosynthetic capacity and carbon-n itrogen ratio of new leaves of most plant species did not change. Whil e the ecosystem now loses N, the long-term fate of soil N is a key unc ertainty in predicting the future response of boreal ecosystems to cli mate change.