Winter respiratory activity of soils from Bouteloua gracilis dominated grassland of southwestern Alberta was examined, both under in situ field conditions and over a matrix of defined laboratory conditions. The effect of winter thaw conditions was very pronounced on observed rates of soil surface CO 2 evolution. Under conditions of diurnally fluctuating air temperatures, from ca. −18 to +8 °C, soil surface temperatures in early January ranged from ca. −12 to +4 °C, while concurrently measured respiratory activity ranged from less than 2 to over 16 mg CO 2 ∙m −2 ∙h −1 . By early spring, soil surface heating was even more extreme as a result of the greater magnitude of midday insolation exposure, with observed mean values of CO 2 release ranging from less than 10 to over 60 mg CO 2 ∙m −2 ∙h −1 . Laboratory incubations showed continued, although low rates of respiratory activity in soils held at subzero temperatures, with a marked biphasic response pattern evident in Arrhenius plots of soil respiration. Predicted cumulative soil surface CO 2 release was estimated at 34–48 g CO 2 ∙m −2 , depending on whether the effects of observed postthaw respiratory response were included. Some 55% of overall winter soil respiratory activity in the top 8 cm of the soil profile is predicted to occur at temperatures between −4 and +4 °C, with the remaining respiratory activity largely occurring at temperatures up to 15 °C. This magnitude of soil surface CO 2 release represents between 3 and 30% of previously observed estimates of belowground root mass loss in the winter period, depending on whether this mass loss is presumed to occur over the entire winter period or mainly in early spring, coinciding with the peak period of root exudate production.
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Coxson et al. (1987) studied this question.