Large amounts of labile organic carbon in permafrost soils of northern Alaska

2015 | journal article. A publication with affiliation to the University of Göttingen.

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​Large amounts of labile organic carbon in permafrost soils of northern Alaska​
Mueller, C. W.; Rethemeyer, J.; Kao-Kniffin, J.; Löppmann, S.; Hinkel, K. M. & Bockheim, J. G.​ (2015) 
Global Change Biology21(7) pp. 2804​-2817​.​ DOI: https://doi.org/10.1111/gcb.12876 

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Authors
Mueller, Carsten W.; Rethemeyer, Janet; Kao-Kniffin, Jenny; Löppmann, Sebastian; Hinkel, Kenneth M.; Bockheim, James G.
Abstract
Permafrost-affected soils of the northern circumpolar region represent 50% of the terrestrial soil organic carbon (SOC) reservoir and are most strongly affected by climatic change. There is growing concern that this vast SOC pool could transition from a net C sink to a source. But so far little is known on how the organic matter (OM) in permafrost soils will respond in a warming future, which is governed by OM composition and possible stabilization mechanisms. To investigate if and how SOC in the active layer and adjacent permafrost is protected against degradation, we employed density fractionation to separate differently stabilized SOM fractions. We studied the quantity and quality of OM in different compartments using elemental analysis, C-13 solid-phase nuclear magnetic resonance (C-13-NMR) spectroscopy, and C-14 analyses. The soil samples were derived from 16 cores from drained thaw lake basins, ranging from 0 to 5500years of age, representing a unique series of developing Arctic soils over time. The normalized SOC stocks ranged between 35.5 and 86.2kgSOCm(-3), with the major amount of SOC located in the active layers. The SOC stock is dominated by large amounts of particulate organic matter (POM), whereas mineral-associated OM especially in older soils is of minor importance on a mass basis. We show that tremendous amounts of over 25kgOC per square meter are stored as presumably easily degradable OM rich in carbohydrates. Only about 10kgOC per square meter is present as presumably more stable, mineral-associated OC. Significant amounts of the easily degradable, carbohydrate-rich OM are preserved in the yet permanently frozen soil below the permafrost table. Forced by global warming, this vast labile OM pool could soon become available for microbial degradation due to the continuous deepening of the annually thawing active layer.
Issue Date
2015
Journal
Global Change Biology 
ISSN
1365-2486; 1354-1013
Language
English

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