Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 14
Biogeosciences, 12, 4525–4542, 2015
https://doi.org/10.5194/bg-12-4525-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 4525–4542, 2015
https://doi.org/10.5194/bg-12-4525-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 30 Jul 2015

Research article | 30 Jul 2015

Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic

N. Gentsch1, R. Mikutta1,2, R. J. E. Alves3, J. Barta4, P. Čapek4, A. Gittel5, G. Hugelius6, P. Kuhry6, N. Lashchinskiy7, J. Palmtag6, A. Richter8,9, H. Šantrůčková4, J. Schnecker8,9,10, O. Shibistova1,11, T. Urich3,9, B. Wild8,9,12, and G. Guggenberger1,11 N. Gentsch et al.
  • 1Institute of Soil Science, Leibniz Universität Hannover, Hanover, Germany
  • 2Soil Sciences, Martin Luther Universität Halle-Wittenberg, Halle, Germany
  • 3University of Vienna, Department of Ecogenomics and Systems Biology, Vienna, Austria
  • 4University of South Bohemia, Department of Ecosystems Biology, České Budéjovice, Czech Republic
  • 5Aarhus University, Center for Geomicrobiology, Aarhus, Denmark
  • 6Stockholm University, Department of Physical Geography and Quaternary Geology, Stockholm, Sweden
  • 7Central Siberian Botanical Garden, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia
  • 8University of Vienna, Department of Microbiology and Ecosystem Science, Vienna, Austria
  • 9Austrian Polar Research Institute, Vienna, Austria
  • 10University of New Hampshire, Department of Natural Resources and the Environment, Durham, NH, USA
  • 11V.N. Sukachev Institute of Forest, Siberian Branch of Russian Academy of Sciences, Krasnoyarsk, Russia
  • 12University of Gothenburg, Department of Earth Sciences, Gothenburg, Sweden

Abstract. In permafrost soils, the temperature regime and the resulting cryogenic processes are important determinants of the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils, there is a lack of research assessing pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions, such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels were sampled in 5 m wide soil trenches across the Siberian Arctic to calculate OC and total nitrogen (TN) stocks based on digital profile mapping. Density fractionation of soil samples was performed to distinguish between particulate OM (light fraction, LF, < 1.6 g cm−3), mineral associated OM (heavy fraction, HF, > 1.6 g cm−3), and a mobilizable dissolved pool (mobilizable fraction, MoF). Across all investigated soil profiles, the total OC storage was 20.2 ± 8.0 kg m−2 (mean ± SD) to 100 cm soil depth. Fifty-four percent of this OC was located in the horizons of the active layer (annual summer thawing layer), showing evidence of cryoturbation, and another 35 % was present in the upper permafrost. The HF-OC dominated the overall OC stocks (55 %), followed by LF-OC (19 % in mineral and 13 % in organic horizons). During fractionation, approximately 13 % of the OC was released as MoF, which likely represents a readily bioavailable OM pool. Cryogenic activity in combination with cold and wet conditions was the principle mechanism through which large OC stocks were sequestered in the subsoil (16.4 ± 8.1 kg m−2; all mineral B, C, and permafrost horizons). Approximately 22 % of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared to be the principle source of the dominant HF (63 %) in the subsoil. Despite the unfavourable abiotic conditions, low C / N ratios and high δ13C values indicated substantial microbial OM transformation in the subsoil, but this was not reflected in altered LF and HF pool sizes. Partial least-squares regression analyses suggest that OC accumulates in the HF fraction due to co-precipitation with multivalent cations (Al, Fe) and association with poorly crystalline iron oxides and clay minerals. Our data show that, across all permafrost pedons, the mineral-associated OM represents the dominant OM fraction, suggesting that the HF-OC is the OM pool in permafrost soils on which changing soil conditions will have the largest impact.

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