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| Titel |
Nitrogen isotope fractionation during archaeal ammonia oxidation: Coupled estimates from isotopic measurements of ammonium and nitrite |
| VerfasserIn |
Maria Mooshammer, Michaela Stieglmeier, Barbara Bayer, Lara Jochum, Michael Melcher, Wolfgang Wanek |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096077
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| Publikation (Nr.) |
 EGU/EGU2014-11563.pdf |
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| Zusammenfassung |
| Ammonia-oxidizing archaea (AOA) are ubiquitous in marine and terrestrial environments and
knowledge about the nitrogen (N) isotope effect associated with their ammonia oxidation
activity will allow a better understanding of natural abundance isotope ratios, and therefore N
transformation processes, in the environment. Here we examine the kinetic isotope effect for
ammonia oxidation in a pure soil AOA culture (Ca. Nitrososphaera viennensis) and a marine
AOA enrichment culture. We estimated the isotope effect from both isotopic signatures
of ammonium and nitrite over the course of ammonia oxidation. Estimates of the
isotope effect based on the change in the isotopic signature of ammonium give
valuable insight, because these estimates are not subject to the same concerns (e.g.,
accumulation of an intermediate) as estimates based on isotopic measurements of
nitrite.
Our results show that both the pure soil AOA culture and a marine AOA enrichment
culture have similar but substantial isotope effect during ammonia consumption (31–34 per
mill; based on ammonium) and nitrite production (43–45 per mill; based on nitrite). The 15N
fractionation factors of both cultures tested fell in the upper range of the reported isotope
effects for archaeal and bacterial ammonia oxidation (10–41 per mill) or were even
higher than those. The isotope fractionation for nitrite production was significantly
larger than for ammonium consumption, indicating that (1) some intermediate (e.g.,
hydroxylamine) of ammonia oxidation accumulates, allowing for a second 15N
fractionation step to be expressed, (2) a fraction of ammonia oxidized is lost via
gaseous N forms (e.g., NO or N2O), which is 15N-enriched or (3) a fraction of
ammonium is assimilated into AOA biomass, biomass becoming 15N-enriched. The
significance of these mechanisms will be explored in more detail for the soil AOA
culture, based on isotope modeling and isotopic measurements of biomass and N2O. |
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