Linkages between soil micro-site properties and CO 2 and N 2O emissions during a simulated thaw for a northern prairie Mollisol

Abstract

Biologically derived emissions of carbon dioxide (CO 2) and nitrous oxide (N 2O) at 0 °C vary with soil depth during soil thawing. 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 °C) and sampled for CO 2 and N 2O emissions throughout the soil profile. Emission data were fit to a first order exponential equation (E = αe βT). 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 CO 2 and N 2O emissions at 0 °C declined exponentially with depth. Emissions of CO 2 and N 2O at 0 °C were strongly related to root length (R 2 = 0.80 and 0.76, respectively), root mass (R 2 = 0.56 and 0.74), large macroaggregate mass (R 2 = 0.63 and 0.54), and aggregate-protected organic matter (R 2 > 0.57), while available organic matter was related to CO 2 (R 2 > 0.60) and not N 2O. When CO 2 and N 2O emissions were normalized by available and aggregate-protected carbon pools, respectively, nutrient use efficiency increased significantly with depth. Results suggest CO 2 and N 2O emissions are (1) positively influenced by the rhizosphere and (2) differentially affected by substrate pool or location. CO 2 emissions were more positively affected by available substrate, while N 2O emissions were more positively affected by less labile, aggregate-protected substrate. © 2012 Elsevier Ltd.