@article{fdi:010074938,
  title = {{D}issolved organic matter influences {N}-2 fixation in the {N}ew {C}aledonian lagoon ({W}estern {T}ropical {S}outh {P}acific)},
  author = {{B}enavides, {M}ar and {M}artias, {C}. and {E}lifantz, {H}. and {B}erman-{F}rank, {I}. and {D}upouy, {C}{\'e}cile and {B}onnet, {S}ophie},
  editor = {},
  language = {{ENG}},
  abstract = {{S}pecialized prokaryotes performing biological dinitrogen ({N}-2) fixation ("diazotrophs") provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. {I}n these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non -cyanobacterial diazotrophs are currently unclear. {T}he latter are not photosynthetic (here called "heterotrophic") and hence require external sources of organic matter to sustain {N}-2 fixation. {H}ere we added the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea ({DCMU}) to estimate the {N}-2 fixation potential of heterotrophic diazotrophs as compared to autotrophic ones. {A}dditionally, we explored the influence of dissolved organic matter ({DOM}) on these diazotrophs along a coast to open ocean gradient in the surface waters of a subtropical coral lagoon ({N}ew {C}aledonia). {T}otal {N}-2 fixation (samples not amended with {DCMU}) ranged from 0.66 to 1.32 nmol {N} {L}-1 d(-1). {T}he addition of {DCMU} reduced {N}-2 fixation by >90%, suggesting that the contribution of heterotrophic diazotrophs to overall {N}-2 fixation activity was minor in this environment. {H}igher contribution of heterotrophic diazotrophs occurred in stations closer to the shore and coincided with the decreasing lability of {DOM}, as shown by various colored {DOM} and fluorescent {DOM} ({ODOM} and {FDOM}) indices. {W}e tested the response of diazotrophs (in terms of nif{H} gene expression and bulk {N}-2 fixation rates) upon the addition of a mix of carbohydrates ("{DOC}" treatment), amino acids ("{DON}" treatment), and phosphonates and phosphomonesters ("{DOP}" treatment). {W}hile nif{H} expression increased significantly in {T}richodesmium exposed to the {DOC} treatment, bulk {N}-2 fixation rates increased significantly only in the {DOP} treatment. {T}he lack of nif{H} expression by gammaproteobacteria, in any of the {DOM} addition treatments applied, questions the contribution of non-cyanobacterial diazotrophs to fixed nitrogen inputs in the {N}ew {C}aledonian lagoon. {W}hile the metabolism and ecology of heterotrophic diazotrophs is currently elusive, a deeper understanding of their ecology and relationship with {DOM} is needed in the light of increased {DOM} inputs in coastal zones due to anthropogenic pressure.},
  keywords = {non-cyanobacterial diazotrophs ; nif{H} ; {DCMU} ; {DOM} ; {CDOM} ; {FDOM} ; {NOUVELLE} {CALEDONIE} ; {PACIFIQUE} ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{F}rontiers in {M}arine {S}cience},
  volume = {5},
  numero = {},
  pages = {89 [11 ]},
  year = {2018},
  DOI = {10.3389/fmars.2018.00089},
  URL = {https://www.documentation.ird.fr/hor/fdi:010074938},
}