Environmental and biotic controls over methane flux from Arctic tundra
On the arctic slope of the Brooks Range, Alaska, we conducted a series of field experiments and observations to determine the major environmental and biotic controls over methane flux. Methane flux was more strongly influenced by long-term gradients in soil moisture and vegetation than by plant biomass, species composition, or nutrient availability. Soil temperature and moisture explained 75% of the variance in flux across the vegetation gradient. In wet-meadow tundra, where fluxes were high, plants provided the dominant transport pathway for methane, independent of light levels or photosynthesis, and allowed methane transport past the zone of surface oxidation in these saturated soils. In moist tussock tundra, where fluxes were low, soil-methane profiles indicated soil consumption of atmospheric methane, and the presence of plants had negligible influence on methane flux. The low methane fluxes that we and others have recently measured in moist tussock tundra are 10- to 30-fold lower than published values, leading to a 20 Tg yr−1 discrepancy in estimates of global methane sources, equivalent to 17% of net methane flux attributed to global wetlands. These site differences in methane flux emphasize the need for a more comprehensive data base on methane fluxes from natural ecosystems if we are to better understand the current methane budget.