@article{fdi:010073167,
  title = {{T}ransfer of diazotroph-derived nitrogen to the planktonic food web across gradients of {N}-2 fixation activity and diversity in the western tropical {S}outh {P}acific {O}cean},
  author = {{C}affin, {M}. and {B}erthelot, {H}. and {C}ornet-{B}arthaux, {V}. and {B}arani, {A}. and {B}onnet, {S}ophie},
  editor = {},
  language = {{ENG}},
  abstract = {{B}iological dinitrogen ({N}-2) fixation provides the major source of new nitrogen ({N}) to the open ocean, contributing more than atmospheric deposition and riverine inputs to the {N} supply. {Y}et the fate of the diazotrophderived {N} ({DDN}) in the planktonic food web is poorly understood. {T}he main goals of this study were (i) to quantify how much of {DDN} is released to the dissolved pool during {N}-2 fixation and how much is transferred to bacteria, phytoplankton and zooplankton, and (ii) to compare the {DDN} release and transfer efficiencies under contrasting {N}-2 fixation activity and diversity in the oligotrophic waters of the western tropical {S}outh {P}acific ({WTSP}) {O}cean. {W}e used nanometre-scale secondary ion mass spectrometry (nano{SIMS}) coupled with {N}-15(2) isotopic labelling and flow cytometry cell sorting to track the {DDN} transfer to plankton, in regions where the diazotroph community was dominated by either {T}richodesmium or by {UCYN}-{B}. {A}fter 48 h, 2 similar to 20-40% of the {N}-2 fixed during the experiment was released to the dissolved pool when {T}richodesmium dominated, while the {DDN} release was not quantifiable when {UCYNB} dominated; similar to 7-15% of the total fixed {N} (net {N}-2 fixation + release) was transferred to non-diazotrophic plankton within 48 h, with higher transfer efficiencies (15 +/- 3 %) when {UCYN}-{B} dominated as compared to when {T}richodesmium dominated (9 +/- 3 %). {T}he pico-cyanobacteria {S}ynechococcus and {P}rochlorococcus were the primary beneficiaries of the {DDN} transferred (similar to 65-70 %), followed by heterotrophic bacteria (similar to 23-34 %). {T}he {DDN} transfer in bacteria was higher (34 +/- 7 %) in the {UCYN}-{B}-dominating experiment compared to the {T}richodesmium-dominating experiments (24 +/- 5 %). {R}egarding higher trophic levels, the {DDN} transfer to the dominant zooplankton species was less efficient when the diazotroph community was dominated by {T}richodesmium (similar to 5-9% of the {DDN} transfer) than when it was dominated by {UCYN}-{B} (similar to 28 +/- 13% of the {DDN} transfer). {T}o our knowledge, this study provides the first quantification of {DDN} release and transfer to phytoplankton, bacteria and zooplankton communities in open ocean waters. {I}t reveals that despite {UCYN}-{B} fix {N}-2 at lower rates compared to {T}richodesmium in the {WTSP}, the {DDN} from {UCYN}-{B} is much more available and efficiently transferred to the planktonic food web than the {DDN} originating from {T}richodesmium.},
  keywords = {{PACIFIQUE} {SUD}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {15},
  numero = {12},
  pages = {3795--3810},
  ISSN = {1726-4170},
  year = {2018},
  DOI = {10.5194/bg-15-3795-2018},
  URL = {https://www.documentation.ird.fr/hor/fdi:010073167},
}