@article{fdi:010066984,
  title = {{D}ynamics of {N}-2 fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem : results from the {VAHINE} mesocosm experiment ({N}ew {C}aledonia)},
  author = {{B}onnet, {S}ophie and {B}erthelot, {H}. and {T}urk-{K}ubo, {K}. and {F}awcett, {S}. and {R}ahav, {E}. and {L}'{H}elguen, {S}. and {B}erman-{F}rank, {I}.},
  editor = {},
  language = {{ENG}},
  abstract = {{N}-2 fixation rates were measured daily in large (similar to 50 m(3)) mesocosms deployed in the tropical southwest {P}acific coastal ocean ({N}ew {C}aledonia) to investigate the temporal variability in {N}-2 fixation rates in relation with environmental parameters and study the fate of diazotrophderived nitrogen ({DDN}) in a low-nutrient, low-chlorophyll ecosystem. {T}he mesocosms were fertilized with similar to 0.8 mu {M} dissolved inorganic phosphorus ({DIP}) to stimulate diazotrophy. {B}ulk {N}-2 fixation rates were replicable between the three mesocosms, averaged 18.5 +/- 1.1 nmol {N} {L}-1 d(-1) over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 +/- 1.0 nmol {N} {L}-1 d(-1). {T}hese later rates measured after the {DIP} fertilization are higher than the upper range reported for the global ocean. {D}uring the 23 days of the experiment, {N}-2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon ({POC}), nitrogen ({PON}) and phosphorus ({POP}), and alkaline phosphatase activity, and negatively correlated with {DIP} concen-trations, {DIP} turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. {T}he fate of {DDN} was investigated during a bloom of the unicellular diazotroph {UCYN}-{C} that occurred during the second half of the experiment. {Q}uantification of diazotrophs in the sediment traps indicates that similar to 10 % of {UCYN}-{C} from the water column was exported daily to the traps, representing as much as 22.4 +/- 5.5 % of the total {POC} exported at the height of the {UCYN}-{C} bloom. {T}his export was mainly due to the aggregation of small (5.7 +/- 0.8 mu m) {UCYN}-{C} cells into large (100-500 mu m) aggregates. {D}uring the same time period, a {DDN} transfer experiment based on high-resolution nanometerscale secondary ion mass spectrometry (nano{SIMS}) coupled with {N}-15(2) isotopic labeling revealed that 16 +/- 6 % of the {DDN} was released to the dissolved pool and 21 +/- 4 % was transferred to non-diazotrophic plankton, mainly picoplankton (18 +/- 4 %) followed by diatoms (3 +/- 2 %). {T}his is consistent with the observed dramatic increase in picoplankton and diatom abundances, primary production, bacterial production, and standing stocks of {POC}, {PON}, and {POP} in the mesocosms during the second half of the experiment. {T}hese results offer insights into the fate of {DDN} during a bloom of {UCYN}-{C} in low-nutrient, low-chlorophyll ecosystems.},
  keywords = {{NOUVELLE} {CALEDONIE} ; {PACIFIQUE} ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {13},
  numero = {9},
  pages = {2653--2673},
  ISSN = {1726-4170},
  year = {2016},
  URL = {https://www.documentation.ird.fr/hor/fdi:010066984},
}