@article{fdi:010064829,
  title = {{D}initrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the {VAHINE} mesocosm experiment ({N}ew {C}aledonia lagoon)},
  author = {{B}erthelot, {H}. and {M}outin, {T}. and {L}'{H}elguen, {S}. and {L}eblanc, {K}. and {H}{\'e}lias, {S}. and {G}rosso, {O}. and {L}eblond, {N}. and {C}harri{\`e}re, {B}. and {B}onnet, {S}ophie},
  editor = {},
  language = {{ENG}},
  abstract = {{I}n the oligotrophic ocean characterized by nitrate ({NO}3-) depletion in surface waters, dinitrogen ({N}-2) fixation and dissolved organic nitrogen ({DON}) can represent significant nitrogen ({N}) sources for the ecosystem. {I}n this study, we deployed large in situ mesocosms in {N}ew {C}aledonia in order to investigate (1) the contribution of {N}-2 fixation and {DON} use to primary production ({PP}) and particle export and (2) the fate of the freshly produced particulate organic {N} ({PON}), i.e., whether it is preferentially accumulated and recycled in the water column or exported out of the system. {T}he mesocosms were fertilized with phosphate ({PO}43-) in order to prevent phosphorus ({P}) limitation and promote {N}-2 fixation. {T}he diazotrophic community was dominated by diatom-diazotroph associations ({DDA}s) during the first part of the experiment for 10 days ({P}1) followed by the unicellular {N}-2-fixing cyanobacteria {UCYN}-{C} for the last 9 days ({P}2) of the experiment. {N}2 fixation rates averaged 9.8 +/- 4.0 and 27.7 +/- 8.6 nmol {L}-1 d(-1) during {P}1 and {P}2, respectively. {NO}3- concentrations (<0.04 mu mol {L}-1) in the mesocosms were a negligible source of {N}, indicating that {N}-2 fixation was the main driver of new production throughout the experiment. {T}he contribution of {N}-2 fixation to {PP} was not significantly different (p > 0.05) during {P}1 (9.0 +/- 3.3 %) and {P}2 (12.6 +/- 6.1 %). {H}owever, the e ratio that quantifies the efficiency of a system to export particulate organic carbon ({POC}export) compared to {PP} (e ratio = {POC}export / {PP}) was significantly higher (p < 0.05) during {P}2 (39.7 +/- 24.9 %) than during {P}1 (23.9 +/- 20.2 %), indicating that the production sustained by {UCYN}-{C} was more efficient at promoting {C} export than the production sustained by {DDA}s. {D}uring {P}1, {PON} was stable and the total amount of {N} provided by {N}2 fixation (0.10 +/- 0.02 mu mol {L}-1) was not significantly different (p > 0.05) from the total amount of {PON} exported (0.10 +/- 0.04 mu mol {L}-1), suggesting a rapid and probably direct export of the recently fixed {N}-2 by the {DDA}s. {D}uring {P}2, both {PON} concentrations and {PON} export increased in the mesocosms by a factor 1.5-2. {U}nlike in {P}1, this {PON} production was not totally explained by the new {N} provided by {N}-2 fixation. {T}he use of {DON}, whose concentrations decreased significantly (p < 0.05) from 5.3 +/- 0.5 mu mol {L}-1 to 4.4 +/- 0.5 mu mol {L}-1, appeared to be the missing {N} source. {T}he {DON} consumption (similar to 0.9 mu mol {L}-1) during {P}2 is higher than the total amount of new {N} brought by {N}-2 fixation (similar to 0.25 mu mol {L}-1) during the same period. {T}hese results suggest that while {DDA}s mainly rely on {N}-2 fixation for their {N} requirements, both {N}-2 fixation and {DON} can be significant {N} sources for primary production and particulate export following {UCYN}-{C} blooms in the {N}ew {C}aledonia lagoon and by extension in the {N}-limited oceans where similar events are likely to occur.},
  keywords = {{NOUVELLE} {CALEDONIE} ; {PACIFIQUE}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {12},
  numero = {13},
  pages = {4099--4112},
  ISSN = {1726-4170},
  year = {2015},
  DOI = {10.5194/bg-12-4099-2015},
  URL = {https://www.documentation.ird.fr/hor/fdi:010064829},
}