Cold Season Respiration across a Low Arctic Landscape: the Influence of Vegetation Type, Snow Depth, and Interannual Climatic Variation

Cold season respiration may significantly affect arctic terrestrial ecosystem annual net carbon balances. Here, the influences of vegetation type, experimentally deepened snow, and interannual climatic variation on total cold season CO2 efflux were investigated in a Canadian low arctic site containing dry heath, tall birch understory, birch hummock, and wet sedge ecosystems. Total efflux ranged from 34 to 126 g CO2-C m(-2) among the vegetation types, with the tall birch understory respiring at least twice that of the birch hummock and four times that of either the dry heath or wet sedge. This variation did not correlate with soil temperature differences alone, but instead was attributed to ecosystem-specific interactions between snow depth, vegetation canopy cover, soil temperature, and moisture, as well as differences in plant biomass and litter production. Respiration from the birch hummock site was twice as high in 2006/2007 (the year of relatively warm fall and late winter soil temperature phases) as compared to 2004/2005, and was enhanced by the snow fence treatment only in the latter year. Together, these data demonstrate that cold season CO2 release differs substantially among tundra vegetation types, and strongly suggest that these effluxes can significantly offset growing season carbon gains, resulting in annual net carbon losses in some years.