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| Titel |
Biogeochemical controls and isotopic signatures of nitrous oxide production by a marine ammonia-oxidizing bacterium |
| VerfasserIn |
C. H. Frame, K. L. Casciotti |
| 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 ; 7, no. 9 ; Nr. 7, no. 9 (2010-09-13), S.2695-2709 |
| Datensatznummer |
250004966
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| Publikation (Nr.) |
 copernicus.org/bg-7-2695-2010.pdf |
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| Zusammenfassung |
| Nitrous oxide (N2O) is a trace gas that contributes to the greenhouse
effect and stratospheric ozone depletion. The N2O yield from
nitrification (moles N2O-N produced per mole ammonium-N consumed) has
been used to estimate marine N2O production rates from measured
nitrification rates and global estimates of oceanic export production.
However, the N2O yield from nitrification is not constant. Previous
culture-based measurements indicate that N2O yield increases as
oxygen (O2) concentration decreases and as nitrite (NO2−)
concentration increases. Here, we have measured yields of N2O from
cultures of the marine β-proteobacterium Nitrosomonas marina
C-113a as they grew on low-ammonium (50 μM) media. These yields, which
were typically between 4 × 10−4 and 7 × 10−4 for cultures with cell densities between 2 × 102 and 2.1 × 104 cells ml−1, were lower than previous reports for
ammonia-oxidizing bacteria. The observed impact of O2 concentration
on yield was also smaller than previously reported under all conditions
except at high starting cell densities (1.5 × 106 cells ml−1), where 160-fold higher yields were observed at 0.5% O2
(5.1 μM dissolved O2) compared with 20% O2 (203 μM dissolved O2). At lower cell densities (2 × 102
and 2.1 × 104 cells ml−1), cultures grown under 0.5%
O2 had yields that were only 1.25- to 1.73-fold higher than cultures
grown under 20% O2. Thus, previously reported many-fold increases in
N2O yield with dropping O2 could be reproduced only at cell
densities that far exceeded those of ammonia oxidizers in the ocean. The
presence of excess NO2− (up to 1 mM) in the growth medium also
increased N2O yields by an average of 70% to 87% depending on
O2 concentration. We made stable isotopic measurements on N2O
from these cultures to identify the biochemical mechanisms behind variations
in N2O yield. Based on measurements of δ15Nbulk, site
preference (SP = δ15Nα−δ15Nβ), and
δ18O of N2O (δ18O-N2O), we estimate that nitrifier-denitrification produced between
11% and 26% of N2O from cultures grown under 20% O2 and 43%
to 87% under 0.5% O2. We also demonstrate that a positive
correlation between SP and δ18O-N2O is expected when
nitrifying bacteria produce N2O. A positive relationship between SP
and δ18O-N2O has been observed in environmental N2O
datasets, but until now, explanations for the observation invoked only
denitrification. Such interpretations may overestimate the role of
heterotrophic denitrification and underestimate the role of ammonia oxidation
in environmental N2O production. |
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