Title: Linkages between soil micro-site properties and CO2 and N2O emissions during a simulated thaw for a northern prairie Mollisol Authors
Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2012
Publication Date: March 27, 2012
Citation: Wick, A.F., Phillips, B.L., Liebig, M.A., West, M.S., Daniels, W. 2012. Linkages between soil micro-site properties and CO2 and N2O emissions during a simulated thaw for a northern prairie Mollisol. Soil Biology and Biochemistry. 50:118-125. Interpretive Summary: Emissions of carbon dioxide and nitrous oxide, two important greenhouse gases, vary considerably throughout the soil profile during thawing. While soil temperature, moisture, and nutrient availability affect emission-related biological activity as soils thaw, it is not clear which soil properties most influence carbon dioxide and nitrous oxide emissions in surface and subsoil depths. To address this issue, a study was undertaken to identify soil properties that affected emissions of carbon dioxide and nitrous oxide emissions within an undisturbed prairie soil near Mandan, ND. Intact cores, split into approximately four inch segments to a depth of 32 inches, were analyzed for carbon dioxide and nitrous oxide emissions at 0 degrees Celsius, root length and mass, soil aggregates, and carbon and nitrogen pools. Carbon dioxide and nitrous oxide emissions were found to decline exponentially with increasing soil depth. Root length and mass, large soil aggregates, and aggregate-protected carbon and nitrogen were positively associated with carbon dioxide and nitrous oxide emissions throughout the soil profile. Strong associations between gas emissions and root parameters suggest such emissions are linked to biological processes in the rhizosphere, a zone where improvements in nutrient use efficiency are possible for soils periodically frozen throughout the year.
Technical Abstract: Biologically derived emissions of carbon dioxide and nitrous oxide at 0 degrees Celsius (C) vary with soil depth. Micro-site soil properties, especially those which influence porosity and substrate availability, also vary with depth and may help explain gas emissions. Intact soil cores collected to a depth of 80 cm from an undisturbed prairie Mollisol in central North Dakota were uniformly subjected to distinct temperature steps during a simulated soil thaw (-15 to 5 degrees C) and sampled for carbon dioxide and nitrous oxide emissions throughout the soil profile. Emission data were fit to a first order exponential equation. Cores were then analyzed in 10 cm depth increments for micro-site properties including root length and mass, aggregation, and organic substrate availability (available, aggregate-protected and mineral-bound pools). Both carbon dioxide and nitrous oxide emissions at 0 degrees C exponentially declined with depth and were correlated with root length, root mass and large macroaggregates. Interestingly, aggregate protected organic matter was correlated with both carbon dioxide and nitrous oxide emissions, while available organic matter was correlated with only carbon dioxide. When carbon dioxide and nitrous oxide emissions were normalized by available and aggregate-protected carbon pools, respectively, nutrient use efficiency increased significantly with depth. Strong correlations with root length for both carbon dioxide and nitrous oxide emissions suggest emissions of these gases during thawing are linked to the rhizosphere. Correlations with substrate pools may point to potential differences in substrate use for organisms producing carbon dioxide and nitrous oxide belowground. To be certain, these relationships should also be investigated further in samples where soil structure remains intact.