Winter soil respiration from an Austrian mountain forest

We measured soil respiration in a mountain forest in the Province of Tyrol, Austria, during winter. Although soil respiration constitutes a major part of total carbon (C) flux, direct measurements are often restricted to the growing season. In this study, we present data on winter soil respiration measured as CO2 efflux through the snow cover and the fraction of root respiration through trenching. We compared three methods: (1) a closed dynamic chamber on the snow surface (FChamb), (2) diffusional flux calculation based on the conductance properties of the snow pack and the CO2 concentration gradient between the soil surface and the snow surface (F2Point), (3) diffusional flux calculated on the basis of incrementally measured CO2 concentration profiles through the snow pack (FProbe). Lateral diffusion and retention of CO2 within the snow pack accounted for an average 38% flux underestimation by FChamb. F2Point and FProbe yielded similar C flux estimates, except where ice layers within the snow profile partially blocked CO2 diffusion and led to a non-linear CO2 gradient and an overestimation of the C flux by the F2Point method. The insulating effect of the snow cover kept soil temperatures above freezing, even where air temperatures were far below 0 °C. CO2 efflux was highest in early winter (0.64 ± 0.05 μmol CO2-C m−2 s−1) and decreased until the end of snow cover. Accumulated CO2 efflux from snow-covered soils was 62 g C m−2 or approximately 12% of total annual soil respiration. The contribution of root respiration to total soil respiration varied between 13% and 50% throughout the winter.