Diazotrophic bacteria respond to Saharan dust additions.

Langlois, Rebecca, Mills, Matthew M., Ridame, Celine, Croot, Peter and LaRoche, Julie (2012) Diazotrophic bacteria respond to Saharan dust additions. Open Access Marine Ecology Progress Series, 470 . pp. 1-14. DOI 10.3354/meps10109.

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Abstract

Three bioassay experiments were performed to study the effects of nutrient and Saharan dust additions on natural diazotrophic communities in the tropical North Atlantic Ocean. Samples for nucleic acid analysis were collected at the beginning and end of 48 h incubations. TaqMan probes specific to 7 diazotrophic phylotypes, viz. filamentous cyanobacteria (Trichodesmium spp.), unicellular cyanobacterial (UCYN) Groups A, B, and C, Gamma A and P Proteobacteria, and Cluster III, were used to quantify nifH DNA abundances. N-2 fixation rates were measured in the same experiments using the N-15(2) gas bubble injection method. N-2 fixation was co-limited by P and Fe. Total nifH abundances increased relative to the control with additions of either Fe or P or both in combination. Additions of dissolved N, alone or in combination with phosphate, induced increases in UCYN-A and Gamma A nifH compared with the control. Saharan dust additions significantly stimulated fixation rates. Abundances of all cyanobacterial and Gamma A nifH phylotypes at least doubled after Saharan dust additions where surface water dissolved Fe concentrations were <2 nmol l(-1). Laboratory experiments with cultures of T. erythraeum demonstrated that dust addition promoted colony formation and the persistence of T. erythraeum biomass relative to cultures to which no Fe was added. Our results with both field and laboratory experiments indicate that Saharan dust positively affects diazotrophic phylotype abundances and changes T. erythraeum colony morphology.

Document Type: Article
Additional Information: Diazotrophic bacteria respond to Saharan dust additions The distribution of oceanic dinitrogen fixing organisms (diazotrophs), especially cyanobacteria Trichodesmium spp., is correlated with atmospheric mineral dust deposition. Aerosol dust deposition is the major source of iron to open ocean waters. Langlois and co-workers performed bottle experiments with added nutrients and Saharan dust. They found that gene abundances of all diazotrophic groups at least doubled after Saharan dust additions in waters with low iron concentrations. Laboratory experiments with cultures of Trichodesmium erythraeum grown with or without iron and/or Saharan dust demonstrated that dust addition promoted colony formation and the persistence of T. erythraeum biomass relative to cultures without iron. The field and laboratory experiments both indicate that Saharan dust positively affects diazotroph gene abundance and changes T. erythraeum colony morphology.
Keywords: Nutrient limitation; Nitrogen fixation; North Atlantic; Bioassay; Trichodesmium; UCYN-A; nifH; qPCR; SUBTROPICAL NORTH-ATLANTIC; NITROGEN-FIXATION; TRICHODESMIUM SPP.; N-2 FIXATION; PRIMARY PRODUCTIVITY; IRON FERTILIZATION; MEDITERRANEAN SEA; OCEAN; PHOSPHORUS; LIMITATION
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > Leibniz-Institut für Meereswissenschaften
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.3354/meps10109
ISSN: 0171-8630
Date Deposited: 18 Jan 2013 08:42
Last Modified: 22 Jun 2018 10:13
URI: http://oceanrep.geomar.de/id/eprint/20146

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