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Marine Ecology Progress Series

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MEPS 432:17-29 (2011)  -  DOI:

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

Katie S. Watkins-Brandt1, Ricardo M. Letelier1, Yvette H. Spitz1, Matthew J. Church2, Daniela Böttjer2, Angelicque E. White1,*

1College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
2Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawai’i at Mãnoa, Honolulu, Hawaii, USA
*Corresponding author. Email:

ABSTRACT: 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.

KEY WORDS: Phosphorus · Nitrogen fixation · Dissolved organic matter

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Cite this article as: Watkins-Brandt KS, Letelier RM, Spitz YH, Church MJ, Böttjer D, White AE (2011) Addition of inorganic or organic phosphorus enhances nitrogen and carbon fixation in the ­oligotrophic North Pacific. Mar Ecol Prog Ser 432:17-29.

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