Cold-season Production of CO₂in Arctic Soils: Can Laboratory and Field Estimates Be Reconciled through a Simple Modeling Approach?

Microbial activity in arctic tundra soils has been evaluated through both lab incubations and field flux measurements. To determine whether these different measurement approaches can be directly linked to each other, we developed a simple model of soil microbial CO2 production during the cold season in tussock tundra, moss tundra, and wet meadow tundra in the Alaskan Arctic. The model incorporated laboratory-based estimates of microbial temperature responses at sub-zero temperatures with field measurements of C stocks through the soil profile and daily temperature measurements at the sites. Estimates of total CO2 production overestimated in situ cold season CO2 fluxes for the studied sites by as much as two- to threefold, suggesting that either CO2 produced in situ does not efflux during the cold season or that microbial respiration potentials are constrained by some other factor in situ. Average estimated winter CO2 production was near 120 g C m−2 in moist tundra and 60 g C m−2 in wet meadow tundra. Production was strongly seasonal, with most of the winter CO2 production happening early in the winter, before soils froze completely through. Roughly two-thirds of the total estimated CO2 production was from deep soils, largely mineral soils, in contrast to growing season CO2 dynamics.