RANGELAND AND LIVESTOCK RESOURCE MANAGEMENT
Location: Northern Great Plains Research Laboratory
Title: Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol
Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 21, 2011
Publication Date: January 1, 2012
Citation: Phillips, B.L., Wick, A.F., Liebig, M.A., West, M.S., Daniels, W. 2012. Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol. Soil Biology and Biochemistry. 45:14-22.
Interpretive Summary: Belowground carbon and nitrogen emissions are one of the greatest sources of uncertainty worldwide, as scientists aim to close the global carbon and nitrogen budgets. Temperature is universally important to production of carbon dioxide and nitrous oxide in soils, and emissions are oftentimes associated with thawing events. While most models use emissions data collected near the surface 10-20 cm, emissions below 20 cm contribute a large proportion of total emissions (20-40%). This project aimed to determine if the effect of temperature on carbon dioxide and nitrous oxide during thawing was similar for surface and subsoil depths. We found the temperature effect during thawing was similar at the surface at 15, 30, 45, 60, and 75 cm depth increments. When temperature was near 0°C, emission estimates declined significantly with depth for both gases. All soil depths responded positively to temperature increases from -15 to 5°C, but emissions at 0°C were modulated by depth.
Soil respiration occurs at depths below the surface, but belowground data are lacking to support multilayer models of soil CO2 and N2O emissions. In particular, Q10s for CO2 and N2O within soil profiles are needed to determine if temperature sensitivities calculated at the surface are similar to those belowground. We collected similar, intact soil cores (56% water-filled pore space) 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 CO2 and N2O emissions at 0, 15, 30, 45, 60, and 75 cm depths. A simple first-order exponential model fit observed CO2 and N2O emissions during thawing (R2=0.91 and 0.99, respectively) but not during freezing. Emissions during freezing were similar to the sterilized core. Parameter estimates for emissions when temperature was near 0°C declined significantly with depth for both gases. However, the temperature responses were similar across depths for CO2 and for N2O, with Q10=4.8 for CO2 and Q10=13.7 for N2O. Differences in emissions with soil depth when temperature was near 0°C indicated soil properties influenced emissions. Similar temperature responses during thawing at multiple depths suggest the temperature sensitivity during thawing was precipitated by the phase change from ice to liquid water.