Response of Tundra CH4 and CO2 Flux to Manipulation of Temperature and Vegetation

We conducted plant species removals, air temperature manipulations, and vegetation and soil transplants in Alaskan wet-meadow and tussock tundra communities to determine the relative importance of vegetation type and environmental variables in controlling ecosystem methane (CH4) and carbon dioxide (CO2) flux. Plastic greenhouses placed over wet-meadow tundra increased air temperature, soil temperature, and soil moisture, but did not affect CH4 or CO2 flux (measured in the dark). By contrast, removal of sedges in the wet meadow significantly decreased flux of CH4, while moss removal tended to increase CH4 emissions. At 15 cm depth, pore-water CH4 concentrations were higher in sedge-removal than in control plots, suggesting that sedges contribute to CH4 emissions by transporting CH4 from anaerobic soil to the atmosphere, rather than by promoting methanogenesis. In reciprocal-ecosystem transplants between the wet-meadow and tussock tundra communities, CH4 and CO2 emissions were higher overall in the wet-meadow site, but were unrelated to transplant origin. Methane flux was correlated with local variation in soil temperature, thaw depth, and water-table depth, but the relative importance of these factors varied through the season. Our results suggest that future changes in CH4 and CO2 flux in response to climatic change will be more strongly mediated by large-scale changes in vegetation and soil parameters than by direct temperature effects.