RESPONSE OF TUNDRA CH4 AND CO2 FLUX TO MANIPULATION OF TEMPERATURE AND VEGETATION

We conducted plant species removals, air temperature manipulations, an d vegetation and soil transplants in Alaskan wet-meadow and tussock tu ndra communities to determine the relative importance of vegetation ty pe and environmental variables in controlling ecosystem methane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-mea dow tundra increased air temperature, soil temperature, and soil moist ure, but did not affect CH4 or CO2 flux (measured in the dark). By con trast, removal of sedges in the wet meadow significantly decreased flu x of CH4, while moss removal tended to increase CH4 emissions. At 15 c m depth, pore-water CH4 concentrations were higher in sedge-removal th an in control plots, suggesting that sedges contribute to CH4 emission s by transporting CH4 from anaerobic soil to the atmosphere, rather th an by promoting methanogenesis. In reciprocal-ecosystem transplants be tween the wet-meadow and tussock tundra communities, CH4 and CO2 emiss ions were higher overall in the wet-meadow site, but were unrelated to transplant origin. Methane flux was correlated with local variation i n soil temperature, thaw depth, and water-table depth, but the relativ e importance of these factors varied through the season. Our results s uggest that future changes in CH4 and CO2 flux in response to climatic change will be more strongly mediated by large-scale changes in veget ation and soil parameters than by direct temperature effects.