Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol

Abstract The fate of carbon (C) and nitrogen (N) belowground is important to current and future climate models as soils warm in northern latitudes. Currently, little is known about the sensitivity of microbial respiration to temperature changes at depths below 15 cm. We used whole-core (7.6 cm dia. × 90 cm) laboratory incubations to determine if temperature response quotients ( Q 10 ) for CO 2 and N 2 O varied with depth for undisturbed prairie while plants were senescent and clipped at the surface. We collected intact soil cores from an undisturbed prairie in central North Dakota and uniformly subjected them to freezing (5 to −15 °C) and thawing (−15 to 5 °C). We measured rates of CO 2 and N 2 O emissions at 5 °C temperature increments at 0, 15, 30, 45, 60, and 75 cm depths. During freezing, active and sterilized core emissions occurred only between 0 and −10 °C. During thawing, a simple first-order exponential model, E  = αe βT , fit observed CO 2 and N 2 O emissions ( R 2  = 0.91 and 0.99, respectively). Parameter estimates for β were not significantly different across depths for CO 2 and for N 2 O ( Q 10  = 4.8 and 13.7, respectively). Parameter estimates for α (emissions when temperature is 0 °C) exponentially declined with depth for both gases for similar depth-response curves. Stepwise regressions of soil properties on α parameter estimates indicated emissions of CO 2 and N 2 O at 0 °C during thawing were positively correlated ( R 2  > 0.6) with soil porosity. Results indicate pedogenic properties associated with depth may not necessarily influence temperature response curves during thawing but will affect emissions at 0 °C for both CO 2 and N 2 O.