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| Titel |
Storage and transformation of organic matter fractions in cryoturbated permafrost soils across the Siberian Arctic |
| VerfasserIn |
N. Gentsch, R. Mikutta, R. J. E. Alves, J. Barta, P. Čapek, A. Gittel, G. Hugelius, P. Kuhry, N. Lashchinskiy, J. Palmtag, A. Richter, H. Šantrůčková, J. Schnecker, O. Shibistova, T. Urich, B. Wild, G. Guggenberger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 14 ; Nr. 12, no. 14 (2015-07-30), S.4525-4542 |
| Datensatznummer |
250118043
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| Publikation (Nr.) |
 copernicus.org/bg-12-4525-2015.pdf |
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| Zusammenfassung |
| 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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