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| Titel |
Autotrophic fixation of geogenic CO2 by microorganisms contributes to soil organic matter formation and alters isotope signatures in a wetland mofette |
| VerfasserIn |
M. E. Nowak, F. Beulig, J. von Fischer, J. Muhr, K. Küsel, S. E. Trumbore |
| 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. 23 ; Nr. 12, no. 23 (2015-12-08), S.7169-7183 |
| Datensatznummer |
250118205
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| Publikation (Nr.) |
 copernicus.org/bg-12-7169-2015.pdf |
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| Zusammenfassung |
To quantify the contribution of autotrophic microorganisms to organic matter (OM)
formation in soils, we investigated natural CO2 vents (mofettes)
situated in a wetland in northwest Bohemia (Czech Republic). Mofette soils had
higher soil organic matter (SOM) concentrations than reference soils due to restricted
decomposition under high CO2 levels. We used radiocarbon (Δ14C)
and stable carbon (δ13C) isotope ratios to
characterize SOM and its sources in two mofettes and compared it with
respective reference soils, which were not influenced by geogenic CO2.
The geogenic CO2 emitted at these sites is free of radiocarbon and
enriched in 13C compared to atmospheric CO2. Together, these
isotopic signals allow us to distinguish C fixed by plants from C fixed by
autotrophic microorganisms using their differences in 13C
discrimination. We can then estimate that up to 27 % of soil organic
matter in the 0–10 cm layer of these soils was derived from microbially
assimilated CO2.
Isotope values of bulk SOM were shifted towards more positive δ13C
and more negative Δ14C values in mofettes compared to
reference soils, suggesting that geogenic CO2 emitted from the soil
atmosphere is incorporated into SOM. To distinguish whether geogenic
CO2 was fixed by plants or by CO2 assimilating microorganisms, we
first used the proportional differences in radiocarbon and δ13C
values to indicate the magnitude of discrimination of the stable isotopes in
living plants. Deviation from this relationship was taken to indicate the
presence of microbial CO2 fixation, as microbial discrimination should
differ from that of plants. 13CO2-labelling experiments confirmed
high activity of CO2 assimilating microbes in the top 10 cm, where
δ13C values of SOM were shifted up to 2 ‰
towards more negative values. Uptake rates of microbial CO2 fixation
ranged up to 1.59 ± 0.16 μg gdw−1 d−1. We inferred
that the negative δ13C shift was caused by the activity of
autotrophic microorganisms using the Calvin–Benson–Bassham (CBB) cycle, as
indicated from quantification of cbbL/cbbM marker genes encoding for RubisCO
by quantitative polymerase chain reaction (qPCR) and by acetogenic and
methanogenic microorganisms, shown present in the mofettes by previous
studies. Combined Δ14C and δ13C isotope mass
balances indicated that microbially derived carbon accounted for 8–27 %
of bulk SOM in this soil layer.
The findings imply that autotrophic microorganisms can recycle significant
amounts of carbon in wetland soils and might contribute to observed
radiocarbon reservoir effects influencing Δ14C signatures in
peat deposits. |
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