Soil CO2 efflux vs. soil respiration: Implications for flux models

Abstract

In the long term, all CO2 produced in the soil must be emitted by the surface and soil CO2 efflux (FCO2) must correspond to soil respiration (Rsoil). In the short term, however, the efflux can deviate from the instantaneous soil respiration, if the amount of CO2 stored in the soil pore-space (SCO2) is changing. We measured FCO2 continuously for one year using an automated chamber system. Simultaneously, vertical soil profiles of CO2 concentration, moisture, and temperature were measured in order to assess the changes in the amount of CO2 stored in the soil. Rsoil was calculated as the sum of the rate of change of the CO2 storage over time and FCO2. The experiment was split into a warm and a cold season. The dependency of soil respiration and soil efflux on soil temperature and on soil moisture was analyzed separately. Only the moisture-driven model of the warm season was significantly different for FCO2 and Rsoil. At our site, a moisture-driven soil-respiration model derived from CO2 efflux data would underestimate the importance of soil moisture. This effect can be attributed to a temporary storage of CO2 in the soil pore-space after rainfalls where up to 40% of the respired CO2 were stored.