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Penning, H. ; Conrad, R.*

Quantification of carbon flow from stable isotope fractionation in rice field soils with different organic matter content.

Org. Geochem. 38, 2058-2069 (2007)
DOI
Open Access Green as soon as Postprint is submitted to ZB.
Rice fields are an important source for the greenhouse gas methane produced by acetoclastic and hydrogenotrophic methanogenesis. Fractionation of 13C/12C can in principle be used to quantify the relative contribution of these pathways, but our knowledge of isotopic fractionation during reduction of CO2 and turnover of acetate in different methanogenic environments is still scarce. We therefore measured ?13C signatures in two types of anoxic Italian rice field soils, one with high and one with low degradable organic matter (OM) content. Both soils were incubated in the presence and absence of methyl fluoride, a specific inhibitor of acetoclastic methanogenesis. Optimization of methyl fluoride concentration resulted in complete inhibition of acetoclastic methanogenesis. CH4 was then exclusively produced by hydrogenotrophic methanogenesis, allowing determination of the isotopic signatures and fractionation factors specific for this methanogenic pathway. Acetate, which was then no longer consumed, accumulated and was used for determination of the isotopic signature of the fermentatively produced acetate (both total acetate and methyl carbon of acetate). Hence, all isotopic signatures, including fractionation factors were determined for the methanogenic soil. These data, were then used for computation of the relative contribution of the two methanogenic pathways. In the high OM soil, the contribution of acetoclastic methanogenesis to total CH4 production increased simultaneously with decreasing acetate concentration. In the low OM soil, methanogenesis from H2/CO2 was clearly greater than theoretically expected. Furthermore, isotope fractionation of hydrogenotrophic methanogenesis indicated that the in situ energy status of methanogens strongly depended on the availability of organic carbon in the rice field soil system. Collectively, our data show that the study of isotopic fractionation in methanogenic environments allows a deeper insight into the ongoing processes, which may be quite different in the same ecosystem with different content of degradable OM.
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Publication type Article: Journal article
Document type Scientific Article
Corresponding Author
ISSN (print) / ISBN 0146-6380
e-ISSN 1873-5290
Journal Organic Geochemistry
Quellenangaben Volume: 38, Issue: 12, Pages: 2058-2069 Article Number: , Supplement: ,
Publisher Elsevier
Non-patent literature Publications
Reviewing status Peer reviewed
Institute(s) Institute of Groundwater Ecology (IGOE)