Changes in latitude and dominant diazotrophic community alter N<inf>2</inf> fixation

Raes, EJ; Waite, AM; McInnes, AS; Olsen, H; Nguyen, HM; Hardman-Mountford, N; Thompson, PA

Changes in latitude and dominant diazotrophic community alter N<inf>2</inf> fixation

Raes, EJ Waite, AM McInnes, AS

Olsen, H Nguyen, HM Hardman-Mountford, N Thompson, PA

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Publication Type:: Journal Article
Citation:: Marine Ecology Progress Series, 2014, 516 pp. 85 - 102
Issue Date:: 2014-12-03

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Field	Value	Language
dc.contributor.author	Raes, EJ	en_US
dc.contributor.author	Waite, AM	en_US
dc.contributor.author	McInnes, AS https://orcid.org/0000-0002-8340-3133	en_US
dc.contributor.author	Olsen, H	en_US
dc.contributor.author	Nguyen, HM	en_US
dc.contributor.author	Hardman-Mountford, N	en_US
dc.contributor.author	Thompson, PA	en_US
dc.date.issued	2014-12-03	en_US
dc.identifier.citation	Marine Ecology Progress Series, 2014, 516 pp. 85 - 102	en_US
dc.identifier.issn	0171-8630	en_US
dc.identifier.uri	http://hdl.handle.net/10453/35860
dc.description.abstract	© Inter-Research 2014 The contribution of planktonic diazotrophs to the overall N budget is a key unknown in the eastern Indian Ocean. Here we investigated the relationships between dissolved inorganic nutrients, phytoplankton pigment composition, microbial community structure, nitrogen fixation rates and the δ15N of fractionated zooplankton samples along the shelf break of Western Australia (32° to 12° S) in September 2012. Bulk nitrogen fixation rates declined from 4.8 nmol l-1 h-1 in the colder and more saline sub-tropical waters at higher latitudes to 1.5 nmol l-1 h-1 in the warmer and fresher Timor Sea at lower latitudes. A regional bloom of Trichodesmium was identified between 13° and 9° S in the Timor Sea. Trichodesmium-specific N2 fixation rates were 0.05 ± 0.01 nmol colony-1 h-1. Highest dissolved inorganic nitrogen (DIN) concentrations occurred at the highest NH4+:NO3- ratios, thereby deviating from the paradigm that greater DIN concentrations come primarily from increased NO3- through advection, mixing or upwelling. Both the microplankton and nanoflagellate fraction declined significantly in warmer waters, with higher DIN concentrations but decreasing % NO3-. A clear increase in the prokaryotic diagnostic pigment zeaxanthin was seen with increasing temperatures from higher to lower latitudes. The microbial community, measured using automated ribosomal intergenic spacer analysis (ARISA), clustered strongly according to the water mass biogeochemistry including temperature, salinity, DIN and phosphate concentrations (p < 0.001). Isotope analysis suggested that injections of low δ15N from N2 fixation lowered the zooplankton δ15N signature of animals up to ∼500 μm in size and that nearly 47% of the fixed nitrogen was used by zooplankton (≤500 μm fraction) in the Timor Sea.	en_US
dc.relation.ispartof	Marine Ecology Progress Series	en_US
dc.relation.isbasedon	10.3354/meps11009	en_US
dc.subject.classification	Marine Biology & Hydrobiology	en_US
dc.title	Changes in latitude and dominant diazotrophic community alter N<inf>2</inf> fixation	en_US
dc.type	Journal Article
utslib.citation.volume	516	en_US
utslib.for	0602 Ecology	en_US
utslib.for	0608 Zoology	en_US
utslib.for	0405 Oceanography	en_US
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Science
utslib.copyright.status	open_access
pubs.publication-status	Published	en_US
pubs.volume	516	en_US

Abstract:

© Inter-Research 2014 The contribution of planktonic diazotrophs to the overall N budget is a key unknown in the eastern Indian Ocean. Here we investigated the relationships between dissolved inorganic nutrients, phytoplankton pigment composition, microbial community structure, nitrogen fixation rates and the δ15N of fractionated zooplankton samples along the shelf break of Western Australia (32° to 12° S) in September 2012. Bulk nitrogen fixation rates declined from 4.8 nmol l-1 h-1 in the colder and more saline sub-tropical waters at higher latitudes to 1.5 nmol l-1 h-1 in the warmer and fresher Timor Sea at lower latitudes. A regional bloom of Trichodesmium was identified between 13° and 9° S in the Timor Sea. Trichodesmium-specific N2 fixation rates were 0.05 ± 0.01 nmol colony-1 h-1. Highest dissolved inorganic nitrogen (DIN) concentrations occurred at the highest NH4+:NO3- ratios, thereby deviating from the paradigm that greater DIN concentrations come primarily from increased NO3- through advection, mixing or upwelling. Both the microplankton and nanoflagellate fraction declined significantly in warmer waters, with higher DIN concentrations but decreasing % NO3-. A clear increase in the prokaryotic diagnostic pigment zeaxanthin was seen with increasing temperatures from higher to lower latitudes. The microbial community, measured using automated ribosomal intergenic spacer analysis (ARISA), clustered strongly according to the water mass biogeochemistry including temperature, salinity, DIN and phosphate concentrations (p < 0.001). Isotope analysis suggested that injections of low δ15N from N2 fixation lowered the zooplankton δ15N signature of animals up to ∼500 μm in size and that nearly 47% of the fixed nitrogen was used by zooplankton (≤500 μm fraction) in the Timor Sea.

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