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.