Response of tundra CH4 and CO2 flux tomanipulation of temperature and vegetation

We conducted plant species removals, air temperaturemanipulations, and vegetation and soil transplants inAlaskan wet-meadow and tussock tundra communities todetermine the relative importance of vegetation typeand environmental variables in controlling ecosystemmethane (CH₄) and carbon dioxide (CO₂) flux. Plastic greenhouses placed over wet-meadow tundraincreased air temperature, soil temperature, and soilmoisture, but did not affect CH₄ or CO₂ flux(measured in the dark). By contrast, removal ofsedges in the wet meadow significantly decreased fluxof CH₄, while moss removal tended to increaseCH₄ emissions. At 15 cm depth, pore-waterCH₄ concentrations were higher in sedge-removalthan in control plots, suggesting that sedgescontribute to CH₄ emissions by transportingCH₄ from anaerobic soil to the atmosphere, ratherthan by promoting methanogenesis. Inreciprocal-ecosystem transplants between thewet-meadow and tussock tundra communities, CH₄and CO₂ emissions were higher overall in thewet-meadow site, but were unrelated to transplantorigin. Methane flux was correlated with localvariation in soil temperature, thaw depth, andwater-table depth, but the relative importance ofthese factors varied through the season. Our resultssuggest that future changes in CH₄ and CO₂flux in response to climatic change will be morestrongly mediated by large-scale changes in vegetationand soil parameters than by direct temperature effects.