Addition of inorganic or organic phosphorus enhances nitrogen and carbon fixation in the oligotrophic North Pacific Public Deposited

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  • We present a spatially extensive record of dinitrogen (N₂) fixation rates and distributions of N₂ fixing microorganisms along with the results of exogenous phosphorus (P) addition experiments conducted during a series of cruises in the North Pacific Subtropical Gyre (NPSG). We measured the N₂ and carbon (C) fixation rates of natural plankton assemblages in response to the addition of methylphosphonate (MPn), a dissolved organic phosphorus (DOP) compound, and dissolved inorganic phosphorus (DIP). Results are compared to parallel unamended controls. These experiments produced 3 major findings: (1) MPn and DIP were utilized with equal metabolic efficiency over a single photoperiod, (2) the bulk of the enhanced N2 fixation rates were within the range of those previously reported in the NPSG, suggesting that P levels in this region can be saturating but were not at the time of sampling and (3) MPn and DIP additions stimulated C fixation rates beyond estimated contributions by diazotrophs, and hence both DIP and bioavailable DOP additions could lead to enhancement of net primary productivity on short time-scales. Our results suggest that the rate of N₂ fixation in our study region may have been restricted by the availability and/or the composition of the total P pool (inorganic and organic P) during our field season.
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  • Watkins-Brandt, K. S., Letelier, R. M., Spitz, Y. H., Church, M. J., Böttjer, D., & White, A. E. (2011, June 27). Addition of inorganic or organic phosphorus enhances nitrogen and carbon fixation in the oligotrophic North Pacific. Marine Ecology Progress Series, 432, 17-29. doi:10.3354/meps09147
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  • 432
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  • Support for this project was provided by the National Science Foundation (OCE-0623596 and OCE- 0850827).



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