Distribution and drivers of symbiotic and free-living diazotrophic cyanobacteria in the Western Tropical South Pacific

Type Article
Date 2018-03
Language English
Author(s) Stenegren Marcus1, Caputo Andrea1, Berg Carlo2, Bonnet Sophie3, 4, 5, Foster Rachel A.1
Affiliation(s) 1 : Stockholm Univ, Dept Ecol Environm & Plant Sci, Stockholm, Sweden.
2 : Linnaeus Univ, Dept Biol & Environm Sci, Sci Life Lab, Kalmar, Sweden.
3 : Aix Marseille Univ, CNRS, Marseille, France.
4 : Aix Marseille Univ, CNRS, Noumea, New Caledonia.
5 : Inst Rech Dev, Mediterranean Inst Oceanog, Marseille, France.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-03 , Vol. 15 , N. 5 , P. 1559-1578
DOI 10.5194/bg-15-1559-2018
WOS© Times Cited 35
Note Special issue Interactions between planktonic organisms and biogeochemical cycles across trophic and N2 fixation gradients in the western tropical South Pacific Ocean: a multidisciplinary approach (OUTPACE experiment) Editor(s): T. Moutin, S. Bonnet, K. Richards, D. G. Capone, E. Marañón, and L. Mémery
Abstract

The abundance and distribution of cyanobacterial diazotrophs were quantified in two regions (Melanesian archipelago, MA and subtropical gyre, SG) of the Western Tropical South Pacific using nifH qPCR assays. UCYN-A1 and A2 host populations were quantified using 18S rRNA qPCR assays including one newly developed assay. All phylotypes were detected in the upper photic zone (0–50 m), with higher abundances in the MA region. Trichodesmium and UCYN-B dominated, composing 81–100 % of nifH copies detected. Het-1 was the next most abundant, and co-occurred with het-2 and het-3. The two UCYN-A lineages were least abundant (<1.0–1.5 % of total nifH copies) and poorly detected (> 47 %). Abundance of the UCYN-A hosts mirrored their respective symbionts; UCYN-A1 and A2 however were detected while their respective hosts were below detection, suggesting a lower partner fidelity or free-living life history. Pairwise comparisons of abundance and environmental parameters supported two groups: deep (45 m) comprised of UCYN-A and surface (0–15m) comprised of Trichodesmium, het-1 and het-2, while UCYN-B overlapped. Temperature, salinity, and PAR, were positively correlated with the latter abundances except UCYN-A. Similar results were identified in a meta-analysis of 11 external datasets. Combined, our results indicate that conditions favoring the UCYN-A symbiosis differ from those of diatom diazotroph associations and free-living diazotrophs.

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Discussion paper 46 1 MB Open access
Figure S1a-d. Representative standard curves for qPCR and results from specificity experiments 24 830 KB Open access
Final revised paper 20 2 MB Open access
Supplement final paper 1 49 KB Open access
Supplement Figures and Tables Final paper 812 KB Open access
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