Interactive effects of fire, soil, climate, and moss on CO₂ fluxes in black spruce ecosystems of interior Alaska

Abstract

We present findings from two complementary studies that examine how fire modifies soil organic matter properties, and how these modifications influence rates of decomposition and carbon (C) exchange in black spruce (Picea mariana) ecosystems of interior Alaska. Our laboratory study showed that burning reduced the sensitivity of decomposition to increased temperature, most likely by inducing moisture or substrate quality limitations on decomposition rates. Burning also reduced the decomposability of Sphagnum-derived organic matter, increased the hydrophobicity of feather-moss-derived organic matter, and increased the ratio of dissolved organic carbon (DOC) to total dissolved nitrogen (TDN) in both the upland and peatland sites. At the ecosystem scale, our field measurements indicate that the surface organic soil was generally wetter in burned than in unburned sites, whereas soil temperature was not different between the burned and unburned sites. Analysis of variance results showed that ecosystem respiration (ER) varied with soil drainage class but not by burn status. However, a more complex general linear model showed that ER was controlled by an interaction between soil temperature, moisture, and burn status, and in general was less variable over time in the burned than in the unburned sites. Together, findings from these studies across different spatial scales suggest that although fire can create some soil climate conditions more conducive to rapid decomposition, rates of C release from soils may be constrained following fire by changes in moisture and/or substrate quality that impede rates of decomposition.

Citation

O'Donnell, J.A.; Turetsky, M.R.; Harden, J.W.; Manies, K.L.; Pruett, L.E.; Shetler, G.; Neff, J.C. 2009. Interactive effects of fire, soil, climate, and moss on CO₂ fluxes in black spruce ecosystems of interior Alaska. Ecosystems. 12: 57-72.