Interactive Effects of Fire, Soil Climate, and Moss on CO2 Fluxes in Black Spruce Ecosystems of Interior Alaska |
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Authors: | Jonathan A O’Donnell Merritt R Turetsky Jennifer W Harden Kristen L Manies Lee E Pruett Gordon Shetler Jason C Neff |
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Institution: | Jonathan A. O’Donnell, Merritt R. Turetsky, Jennifer W. Harden, Kristen L. Manies, Lee E. Pruett, Gordon Shetler and Jason C. Neff |
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Abstract: | Fire is an important control on the carbon (C) balance of the boreal forest region. Here, 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 C exchange in black spruce (Picea mariana) ecosystems of interior Alaska. First, we used laboratory incubations to explore soil temperature, moisture, and vegetation
effects on CO2 and DOC production rates in burned and unburned soils from three study regions in interior Alaska. Second, at one of the
study regions used in the incubation experiments, we conducted intensive field measurements of net ecosystem exchange (NEE)
and ecosystem respiration (ER) across an unreplicated factorial design of burning (2 year post-fire versus unburned sites)
and drainage class (upland forest versus peatland sites). 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 ER varied with
soil drainage class but not by burn status, averaging 0.9 ± 0.1 and 1.4 ± 0.1 g C m−2 d−1 in the upland and peatland sites, respectively. 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.
Author contributions: JAO: performed research, analyzed data, contributed new methods, wrote the paper; MRT: designed laboratory study, performed
research, analyzed data; JWH: designed field study, performed research; KLM: performed research; LEP: performed research,
contributed new method; GS: performed research; JCN: performed research. |
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Keywords: | fire carbon fluxes boreal forest decomposition Alaska climate change |
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