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| Titel |
Storage and stability of organic carbon in soils as related to depth, occlusion within aggregates, and attachment to minerals |
| VerfasserIn |
M. Schrumpf, K. Kaiser, G. Guggenberger, T. Persson, I. Kögel-Knabner, E.-D. Schulze |
| 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 ; 10, no. 3 ; Nr. 10, no. 3 (2013-03-13), S.1675-1691 |
| Datensatznummer |
250018148
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| Publikation (Nr.) |
 copernicus.org/bg-10-1675-2013.pdf |
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| Zusammenfassung |
Conceptual models suggest that stability of organic carbon (OC) in soil
depends on the source of plant litter, occlusion within aggregates,
incorporation in organo-mineral complexes, and location within the soil
profile. Density fractionation is a useful tool to study the relevance of OC
stabilization in aggregates and in association with minerals, but it has
rarely been applied to full soil profiles. We aim to determine factors
shaping the depth profiles of physically unprotected and mineral associated
OC and test their relevance for OC stability across a range of European soils
that vary in vegetation, soil types, parent material, and land use. At each
of the 12 study sites, 10 soil cores were sampled to 60 cm depth and
subjected to density separation. Bulk soil samples and density fractions
(free light fractions – fLF, occluded light fractions – oLF, heavy
fractions – HF) were analysed for OC, total nitrogen (TN), δ14C,
and Δ14C. Bulk samples were also incubated to determine CO2
evolution per g OC in the samples (specific mineralization rates) as an
indicator for OC stability.
Depth profiles of OC in the light fraction (LF-OC) matched those of roots
for undisturbed grassland and forest sites, suggesting that roots are
shaping the depth distribution of LF-OC. Organic C in the HF declined less
with soil depth than LF-OC and roots, especially at grassland sites. The
decrease in Δ14C (increase in age) of HF-OC with soil depth was
related to soil pH as well as to dissolved OC fluxes. This indicates that
dissolved OC translocation contributes to the formation of subsoil HF-OC and
shapes the Δ14C profiles.
The LF at three sites were rather depleted in 14C, indicating the
presence of fossil material such as coal and lignite, probably inherited
from the parent material. At the other sites, modern Δ14C
signatures and positive correlations between specific mineralization rates
and fLF-OC indicate the fLF is a potentially available energy and nutrient
source for subsurface microorganisms throughout the profile. Declining
specific mineralization rates with soil depth confirm greater stability of
OC in subsoils across sites. The overall importance of OC stabilization by
binding to minerals was demonstrated by declining specific mineralization
rates with increasing contributions of HF-OC to bulk soil OC, and the low
Δ14C values of HF-OC. The stability of HF-OC was greater in
subsoils than in topsoils; nevertheless, a portion of HF-OC was active
throughout the profile. While quantitatively less important than OC in the
HF, consistent older ages of oLF-OC than fLF-OC suggest that occlusion of
LF-OC in aggregates also contributes to OC stability in subsoils. Overall,
our results indicate that association with minerals is the most important
factor in stabilization of OC in soils, irrespective of vegetation, soil
type, and land use. |
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