Respiration of recently-fixed plant carbon dominates mid-winter ecosystem CO2 production in sub-arctic heath tundra

Arctic ecosystems could provide a substantial positive feedback to global c limate change if warming stimulates below-ground CO2 release by enhancing d ecomposition of bulk soil organic matter reserves. Ecosystem respiration du ring winter is important in this context because CO2 release from snow-cove red tundra soils is a substantial component of annual net carbon (C) balanc e, and because global climate models predict that the most rapid rises in r egional air temperature will occur in the Arctic during winter. In this man ipulative field study, the relative contributions of plant and bulk soil or ganic matter C pools to ecosystem CO2 production in mid-winter were investi gated. We measured CO2 efflux rates in Swedish sub-arctic heath tundra from control plots and from plots that had been clipped in the previous growing season to disrupt plant activity. Respiration derived from recently-fixed plant C (i.e., plant respiration, and respiration associated with rhizosphe re exudates and decomposition of fresh litter) was the principal source of CO2 efflux, while respiration associated with decomposition of bulk soil or ganic matter was low, and appeared relatively insensitive to temperature. T hese results suggest that warmer mid-winter temperatures in the Arctic may have a much greater impact on the cycling of recently-fixed, plant-associat ed C pools than on the depletion of tundra bulk soil C reserves, and conseq uently that there is a low potential for significant initial feedbacks from arctic ecosystems to climate change during mid-winter.