Photosynthesis of arctic evergreens under snow: Implications for tundra ecosystem carbon balance

Vascular plants are generally assumed to have no photosynthetic activity under the snow because of the severity of the subnivean environment. In the arctic tundra, snow cover persists into the spring after air temperatures and light increase to levels suitable for photosynthesis of vascular plants in the absence of snow cover. We found significant photosynthetic activity in four arctic evergreen species under springtime snow. This activity was facilitated by favorable conditions in the subnivean environment, where CO2 concentrations are elevated, temperatures are often above freezing, and light levels are sufficient to drive photosynthesis. Diurnal changes in CO2 concentration under the snow and light responses of snow-covered ecosystem CO2 fluxes provide supporting evidence of carbon gain at the ecosystem level. This activity allows evergreens to rapidly increase photosynthesis upon snowmelt and reduces wintertime losses of carbon from arctic ecosystems. The loss of these species under predicted scenarios of climate change could have serious implications for tundra carbon balance, potentially increasing carbon losses.