Continuous estimates of CO 2 efflux from arctic and boreal soils during the snow‐covered season in Alaska

Soils in arctic and boreal ecosystems hold large stocks of soil carbon (C), which may be sensitive to changes in climate. Recent studies suggest that winter CO 2 efflux from the subnivean environment may be an important component of annual C budgets in arctic and boreal ecosystems. The present study was designed to examine the seasonal patterns and magnitudes of winter CO 2 efflux from arctic tussock tundra near Toolik Lake, Alaska, and upland boreal forest in Anchorage, Alaska. The seasonal pattern of winter CO 2 efflux differed strongly between the two sites. Tussock tundra showed a prolonged period with very low flux rates between late December and mid‐April. In contrast, rates of CO 2 efflux were relatively high, but variable, throughout the winter at the boreal site. Estimates of C efflux for the snow‐covered season were within the range of previous studies in tussock tundra (24 g C m −2 ) and upland boreal forest (75 g C m −2 ). A simple exponential model, using shallow soil temperatures, explained much of the variation in CO 2 efflux from tussock tundra. In contrast, air temperature was an important secondary control on winter CO 2 efflux from the boreal forest, suggesting that trees became active during prolonged winter thaws. Results of the study imply that warmer winters may increase rates of C efflux from high‐latitude ecosystems. Changes in the depth or duration of snow cover will, however, modulate the relationship between air and soil temperatures and could amplify or dampen the effects of climate warming.