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| Titel |
Fluxes and 13C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought |
| VerfasserIn |
K.-H. Knorr, B. Glaser, C. Blodau |
| 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 ; 5, no. 5 ; Nr. 5, no. 5 (2008-10-28), S.1457-1473 |
| Datensatznummer |
250002839
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| Publikation (Nr.) |
 copernicus.org/bg-5-1457-2008.pdf |
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| Zusammenfassung |
| Peatlands contain a carbon stock of global concern and significantly
contribute to the global methane burden. The impact of drought and rewetting
on carbon cycling in peatland ecosystems is thus currently debated. We
studied the impact of experimental drought and rewetting on intact monoliths
from a temperate fen over a period of ~300 days, using a permanently
wet treatment and two treatments undergoing drought for 50 days. In one of
the mesocosms, vegetation had been removed. Net production of CH4 was
calculated from mass balances in the peat and emission using static chamber
measurements. Results were compared to 13C isotope budgets of CO2
and CH4 and energy yields of acetoclastic and hydrogenotrophic
methanogenesis. Drought retarded methane production after rewetting for days
to weeks and promoted methanotrophic activity. Based on isotope and flux
budgets, aerobic soil respiration contributed 32–96% in the wet
treatment and 86–99% in the other treatments. Drying and rewetting
did not shift methanogenic pathways according to δ13C ratios of
CH4 and CO2. Although δ13C ratios indicated a
prevalence of hydrogenotrophic methanogenesis, free energies of this process
were small and often positive on the horizon scale. This suggests that
methane was produced very locally. Fresh plant-derived carbon input
apparently supported respiration in the rhizosphere and sustained
methanogenesis in the unsaturated zone, according to a 13C-CO2
labelling experiment. The study documents that drying and rewetting in a
rich fen soil may have little effect on methanogenic pathways, but result in
rapid shifts between methanogenesis and methanotrophy. Such shifts may be
promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis
occurred locally even when conditions were not conducive for this process in
the bulk peat. |
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