Abstract:

Winter CO₂ efflux from soils is a significant component of annual carbon budgets and can greatly determine carbon balance of ecosystems. However, present estimates of annual soil respiration are mostly based on measurements taken during the growing season and assume that microbial respiration in frozen or snow-covered soils is negligible. We analyze methods used, magnitude of winter soil respiration, and influencing factors. There are very few measurements of winter soil respiration except in tundra and alpine ecosystems. Winter CO₂ efflux from soils ranged from 0.002 to 1.359 μmol C·m^-2·s^-1 and 0.22 to 0.67 μmol C·m^-2·s^-1 in tundra and forest ecosystems, respectively. No direct relationship between soil temperature and winter CO₂ efflux from soils was found, but there is a critical threshold for active respiration, typically between -7 and -5 ℃, below which lack of free water limits microbial contributions to winter soil respiration. The depth, timing and duration of snow cover greatly influence the magnitude of winter CO₂ efflux from soils, with water availability an important limiting factor. If insulating snowpack is present, carbon availability also controls heterotrophic activity. We discuss current problems and future research needs.

Key words: winter soil respiration, carbon sequestration, snow, tundra, forest