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https://doi.org/10.5194/bg-2020-52
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-52
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Mar 2020

Submitted as: research article | 03 Mar 2020

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This preprint is currently under review for the journal BG.

From fibrous plant residues to mineral-associated organic carbon – the fate of organic matter in Arctic permafrost soils

Isabel Prater1, Sebastian Zubrzycki2, Franz Buegger3, Lena C. Zoor-Füllgraff1, Gerrit Angst4, Michael Dannenmann5, and Carsten W. Mueller1 Isabel Prater et al.
  • 1Technical University of Munich, Research Department Ecology and Ecosystem Management, Soil Science, 85354 Freising, Germany
  • 2University of Hamburg, Center of Earth System Research and Sustainability, School of Integrated Climate System Sciences, 20146 Hamburg, Germany
  • 3Helmholtz Zentrum München, Institute of Biochemical Plant Pathology, 85764 Neuherberg, Germany
  • 4Biology Centre of the Czech Academy of Sciences, Institute of Soil Biology & SoWa Research Infrastructure, 370 05 České Budějovice, Czech Republic
  • 5Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), 82467 Garmisch-Partenkirchen, Germany

Abstract. Permafrost-affected soils of the Arctic account for 70 % or 727 Pg of the soil organic carbon (C) stored in the permafrost region and therefore play a major role in the global C cycle. Most studies on the budgeting of C storage and the quality of soil organic matter (SOM) in the northern circumpolar region focus on bulk soils. Thus, although there is a plethora of assumptions regarding differences in terms of C turnover or stability, only little knowledge is available on the mechanisms stabilizing organic C in Arctic soils besides impaired decomposition due to low temperatures. To gain such knowledge, we investigated soils from Samoylov Island in the Lena River Delta with respect to the composition and distribution of organic C among differently stabilized SOM fractions. The soils were fractionated according to density and particle size to obtain differently stabilized SOM fractions differing in chemical composition and thus bioavailability. To better understand the chemical alterations from plant-derived organic particles in these soils rich in fibrous plant residues to mineral-associated SOM, we analysed the elemental, isotopic and chemical composition of particulate OM (POM) and clay-sized mineral-associated OM (MAOM). We demonstrate that the SOM fractions that contribute with about 17 kg C m−3 for more than 60 % of the C stock are highly bioaccessible and that most of this labile C can be assumed to be prone to mineralization under warming conditions. Thus, the amount of relatively stable, small occluded POM and clay-sized MAOM that account currently with about 10 kg C m−3 for about 40 % of the C stock will most probably be crucial for the quantity of C protected from mineralization in these Arctic soils in a warmer future. Using δ15N as proxy for nitrogen (N) balances indicated an important role of N inputs by biological N fixation, while gaseous N losses appeared less important. However, this could change, as with about 0.4 kg N m−3 one third of the N is present in bioaccessible SOM fractions, which could lead to increases in mineral N cycling and associated N losses under global warming. Our results highlight the vulnerability of SOM in Arctic permafrost-affected soils under rising temperatures, potentially leading to unparalleled greenhouse gas emissions from these soils.

Isabel Prater et al.

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Isabel Prater et al.

Isabel Prater et al.

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Short summary
Large amounts of soil organic matter stored in permafrost-affected soils from Arctic Russia are present as undecomposed plant residues. This large fibrous organic matter might be highly vulnerable to microbial decay, while small mineral-associated organic matter can most probably attenuate carbon mineralization in a warmer future. Labile soil fractions also store large amounts of nitrogen, which might be lost during permafrost collapse while fostering the decomposition of soil organic matter.
Large amounts of soil organic matter stored in permafrost-affected soils from Arctic Russia are...
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