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Chemolithoautotrophic production mediating the cycling of the greenhouse gases N sub(2)O and CH sub(4) in an upwelling ecosystem

The high availability of electron donors occurring in coastal upwelling ecosystems with marked oxyclines favours chemoautotrophy, in turn leading to high N sub(2)O and CH sub(4) cycling associated with aerobic NH sub(4) super(+) (AAO) and CH sub(4) oxidation (AMO). This is the case of the highly pro...

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Bibliographic Details
Published in:Biogeosciences 2009-12, Vol.6 (12), p.3053-3069
Main Authors: Farias, L, Fernandez, C, Faundez, J, Cornejo, M, Alcaman, ME
Format: Article
Language:English
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Summary:The high availability of electron donors occurring in coastal upwelling ecosystems with marked oxyclines favours chemoautotrophy, in turn leading to high N sub(2)O and CH sub(4) cycling associated with aerobic NH sub(4) super(+) (AAO) and CH sub(4) oxidation (AMO). This is the case of the highly productive coastal upwelling area off central Chile (36 S), where we evaluated the importance of total chemolithoautotrophic vs. photoautotrophic production, the specific contributions of AAO and AMO to chemosynthesis and their role in gas cycling. Chemolithoautotrophy was studied at a time-series station during monthly (2007-2009) and seasonal cruises (January 2008, September 2008, January 2009) and was assessed in terms of the natural C isotopic ratio of particulate organic carbon ( delta super(13)POC), total and specific (associated with AAO and AMO) dark carbon assimilation (CA), and N sub(2)O and CH sub(4) cycling experiments. At the oxycline, delta super(13)POC averaged -22.2ppt; this was significantly lighter compared to the surface (-19.7ppt) and bottom layers (-20.7ppt). Total integrated dark CA in the whole water column fluctuated between 19.4 and 2.924 mg C m super(-2) delta super(-1), was higher during active upwelling, and contributed 0.7 to 49.7% of the total integrated autotrophic CA (photo plus chemoautotrophy), which ranged from 135 to 7.626 mg C m super(-2) delta super(-1), and averaged 20.3% for the whole sampling period. Dark CA was reduced by 27 to 48% after adding a specific AAO inhibitor (ATU) and by 24 to 76% with GC7, a specific archaea inhibitor. This indicates that AAO and AMO microbes (most of them archaea) were performing dark CA through the oxidation of NH sub(4) super(+) and CH sub(4). Net N sub(2)O cycling rates varied between 8.88 and 43 nM delta super(-1), whereas net CH sub(4) cycling rates ranged from -0.41 to -2.8 nM delta super(-1). The addition of both ATU and GC7 reduced N sub(2)O accumulation and increased CH sub(4) consumption, suggesting that AAO and AMO were responsible, in part, for the cycling of these gases. These findings show that chemically driven chemolithoautotrophy (with NH sub(4) super(+) and CH sub(4) acting as electron donors) could be more important than previously thought in upwelling ecosystems, raising new questions concerning its relevance in the future ocean.
ISSN:1726-4170
1726-4189