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Temperature response of permafrost soil carbon is attenuated by mineral protection
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. University of Vienna, Austria; Austrian Polar Research Institute, Austria.ORCID iD: 0000-0002-9611-0815
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Number of Authors: 192018 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 24, no 8, p. 3401-3415Article in journal (Refereed) Published
Abstract [en]

Climate change in Arctic ecosystems fosters permafrost thaw and makes massive amounts of ancient soil organic carbon (OC) available to microbial breakdown. However, fractions of the organic matter (OM) may be protected from rapid decomposition by their association with minerals. Little is known about the effects of mineral-organic associations (MOA) on the microbial accessibility of OM in permafrost soils and it is not clear which factors control its temperature sensitivity. In order to investigate if and how permafrost soil OC turnover is affected by mineral controls, the heavy fraction (HF) representing mostly MOA was obtained by density fractionation from 27 permafrost soil profiles of the Siberian Arctic. In parallel laboratory incubations, the unfractionated soils (bulk) and their HF were comparatively incubated for 175 days at 5 and 15 degrees C. The HF was equivalent to 70 +/- 9% of the bulk CO2 respiration as compared to a share of 63 +/- 1% of bulk OC that was stored in the HF. Significant reduction of OC mineralization was found in all treatments with increasing OC content of the HF (HF-OC), clay-size minerals and Fe or Al oxyhydroxides. Temperature sensitivity (Q10) decreased with increasing soil depth from 2.4 to 1.4 in the bulk soil and from 2.9 to 1.5 in the HF. A concurrent increase in the metal-to-HF-OC ratios with soil depth suggests a stronger bonding of OM to minerals in the subsoil. There, the younger C-14 signature in CO2 than that of the OC indicates a preferential decomposition of the more recent OM and the existence of a MOA fraction with limited access of OM to decomposers. These results indicate strong mineral controls on the decomposability of OM after permafrost thaw and on its temperature sensitivity. Thus, we here provide evidence that OM temperature sensitivity can be attenuated by MOA in permafrost soils.

Place, publisher, year, edition, pages
2018. Vol. 24, no 8, p. 3401-3415
Keywords [en]
carbon mineralization, incubation, mineral-organic association, permafrost soils, radiocarbon, temperature sensitivity
National Category
Biological Sciences Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-159020DOI: 10.1111/gcb.14316ISI: 000437284700013PubMedID: 29774972OAI: oai:DiVA.org:su-159020DiVA, id: diva2:1246315
Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-09-07Bibliographically approved

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