Controls on Soil Carbon Dioxide and Methane Fluxes in a Variety of Taiga Forest Stands in Interior Alaska

CO2and CH4fluxes were monitored over 4 years in a range of taiga forests along the Tanana River in interior Alaska. Floodplain alder and white spruce sites and upland birch/aspen and white spruce sites were examined. Each site had control, fertilized, and sawdust amended plots; flux measurements began during the second treatment year. CO2emissions decreased with successional age across the sites (alder, birch/aspen, and white spruce, in order of succession) regardless of landscape position. Although CO2fluxes showed an exponential relationship with soil temperature, the response of CO2production to moisture fit an asymptotic model. Of the manipulations, only N fertilization had an effect on CO2flux, decreasing flux in the floodplain sites but increasing it in the birch/aspen site. Landscape position was the best predictor of CH4flux. The two upland sites consumed CH4at similar rates (approximately$0.5\ {\rm mg}\ {\rm C}\ {\rm m}^{-2}\ {\rm d}^{-1}$), whereas the floodplain sites had lower consumption rates ($0-0.3\ {\rm mg}\ {\rm C}\ {\rm m}^{-2}\ {\rm d}^{-1}$). N fertilization and sawdust both inhibited CH4consumption in the upland birch/aspen and floodplain spruce sites but not in the upland spruce site. The biological processes driving CO2fluxes were sensitive to temperature, moisture, and vegetation, whereas CH4fluxes were sensitive primarily to landscape position and biogeochemical disturbances. Hence, climate change effects on C-gas flux in taiga forest soils will depend on the relationship between soil temperature and moisture and the concomitant changes in soil nutrient pools and cycles.