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| Titel |
Denitrification as the dominant N-elimination process in hydrothermal vents of the Juan de Fuca Ridge, North-East Pacific Ocean |
| VerfasserIn |
Annie Bourbonnais, Moritz F. Lehmann, David A. Butterfield, Steven J. Hallam, Allan H. Devol, Marcel M. M. Kuypers, Gaute Lavik, Réal Roy, Bonnie X. Chang, S. Kim Juniper |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050411
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| Zusammenfassung |
| Nitrogen (N) is an essential macronutrient for all organisms. Therefore, oceanic N sinks,
removing bio-available (or fixed) N, ultimately affect primary productivity. The relative
importance of the two main N-elimination pathways, i.e. denitrification and anaerobic
ammonium oxidation (anammox) in different oceanic environments and in the global
ocean is still a matter of debate. Little is known about metabolic processes and
bacterially-mediated N-cycle dynamics occurring in the subsurface biosphere of
hydrothermal vent systems. Rates of major N-elimination processes have never directly been
quantified in diffuse vent fluids. In this study, we measured rates of major fixed
N-elimination pathways (denitrification, anammox) and dissimilative nitrate reduction to
ammonium (DNRA) in hydrothermal vent fluids at 12 different sites on the Juan de Fuca
Ridge using 15N-label incubations. We also measured the isotopic composition of
dissolved inorganic nitrogen (DIN) (nitrate and ammonium) and N2O concentrations,
an intermediate product of denitrification. Bacteria, Archaea and SUP05 (a group
belonging to the gamma subclass of Proteobacteria that mediates chemolithotrophic
denitrification) SSU rRNA gene copy numbers were determined from DNA extracted from
Sterivex-filtered HV fluids using q-PCR (quantitative polymerase chain reaction) assays. All
samples were collected during cruises in the Northeast Pacific Ocean onboard the
R/V Atlantis in August 2008 and June 2009. Elevated nitrate δ15N and δ18O in the
high-Mg2+, low-T vent fluids associated with a [NO3-] decrease is indicative of
dissimilatory (denitrification) or assimilatory (nitrate uptake) nitrate consumption.
Denitrification rates in hydrothermal vent fluids at Axial Volcano and Endeavour Segment
were high and variable between sites, ranging from ~1 to 1040 nM/day. [N2O]
ranged between ~0-430 nM, with no observable correlation with denitrification
rates. Anammox rates were below ~5 nM/day at 3 sites and not detectable at all
other sites. DNRA rates ranged from ~0 to 200 nM/day. These results suggest that
denitrification is by far the dominant N sink in hydrothermal vent fluids of the Juan de Fuca
Ridge. Furthermore, q-PCR results showed that nitrate reduction associated with
sulfide oxidation is likely an important N-process in hydrothermal vent systems, with
bacteria of the SUP05 cluster representing up to 38% of the total bacterial population.
On-going phylogenetic analysis of the denitrifier functional genes nirS and nirK,
encoding for the nitrite reductase enzyme, together with q-PCR, will allow us to better
characterize the diversity and abundance of sub-seafloor denitrifier populations. |
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