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  Piecewise Structural Equation Model (SEM) Disentangles the Environmental Conditions Favoring Diatom Diazotroph Associations (DDAs) in the Western Tropical North Atlantic (WTNA)

Stenegren, M., Berg, C., Padilla, C. C., David, S.-S., Montoya, J. P., Yager, P. L., et al. (2017). Piecewise Structural Equation Model (SEM) Disentangles the Environmental Conditions Favoring Diatom Diazotroph Associations (DDAs) in the Western Tropical North Atlantic (WTNA). FRONTIERS IN MICROBIOLOGY, 8: 810. doi:10.3389/fmicb.2017.00810.

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 Creators:
Stenegren, Marcus, Author
Berg, Carlo, Author
Padilla, Cory C., Author
David, Stefan-Sebastian1, Author           
Montoya, Joseph P., Author
Yager, Patricia L., Author
Foster, Rachel A.2, Author           
Affiliations:
1Research Group of Chromatin Biochemistry, MPI for Biophysical Chemistry, Max Planck Society, ou_578604              
2Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Max Planck Society, ou_2481693              

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Free keywords: AMAZON RIVER DISCHARGE; MEANDERING GUIANA CURRENT; MARINE NITROGEN-FIXATION; PACIFIC-OCEAN; SURFACE SALINITY; CARBON SEQUESTRATION; EQUATORIAL ATLANTIC; MESOCOSM EXPERIMENT; N-2 FIXATION; CYANOBACTERIAMicrobiology; symbioses; cyanobiont; diatoms; nifH; Amazon; DDAs; piecewise SEM;
 Abstract: Diatom diazotroph associations (DDAs) are important components in the world's oceans, especially in the western tropical north Atlantic (WTNA), where blooms have a significant impact on carbon and nitrogen cycling. However, drivers of their abundances and distribution patterns remain unknown. Here, we examined abundance and distribution patterns for two DDA populations in relation to the Amazon River (AR) plume in the WTNA. Quantitative PCR assays, targeting two DDAs (het-1 and het-2) by their symbiont's nifH gene, served as input in a piecewise structural equation model (SEM). Collections were made during high (spring 2010) and low (fall 2011) flow discharges of the AR. The distributions of dissolved nutrients, chlorophyll-a, and DDAs showed coherent patterns indicative of areas influenced by the AR. A symbiotic Hemiaulus hauckii-Richelia (het-2) bloom (> 10(6) cells L-1) occurred during higher discharge of the AR and was coincident with mesohaline to oceanic (30-35) sea surface salinities (SSS), and regions devoid of dissolved inorganic nitrogen (DIN), low concentrations of both DIP (> 0.1 mu mol L-1) and Si (> 1.0 mu mol L-1). The Richelia (het-1) associated with Rhizosolenia was only present in 2010 and at lower densities (10-1.76 x 10(5) nifH copies L-1) than het-2 and limited to regions of oceanic SSS (> 36). The het-2 symbiont detected in 2011 was associated with H. membranaceus (> 10(3) nifH copies L-1) and were restricted to regions with mesohaline SSS (31.8-34.3), immeasurable DIN, moderate DIP (0.1-0.60 mu mol L-1) and higher Si (4.19-22.1 mu mol L-1). The piecewise SEM identified a profound direct negative effect of turbidity on the het-2 abundance in spring 2010, while DIP and water turbidity had a more positive influence in fall 2011, corroborating our observations of DDAs at subsurface maximas. We also found a striking difference in the influence of salinity on DDA symbionts suggesting a niche differentiation and preferences in oceanic and mesohaline salinities by het-1 and het-2, respectively. The use of the piecewise SEM to disentangle the complex and concomitant hydrography of the WTNA acting on two biogeochemically relevant populations was novel and underscores its use to predict conditions favoring abundance and distributions of microbial populations.

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Language(s): eng - English
 Dates: 2017
 Publication Status: Published online
 Pages: 13
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: ISI: 000401480300003
DOI: 10.3389/fmicb.2017.00810
 Degree: -

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Title: FRONTIERS IN MICROBIOLOGY
Source Genre: Journal
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Publ. Info: PO BOX 110, EPFL INNOVATION PARK, BUILDING I, LAUSANNE, 1015, SWITZERLAND : FRONTIERS MEDIA SA
Pages: - Volume / Issue: 8 Sequence Number: 810 Start / End Page: - Identifier: ISSN: 1664-302X