AME 52:175-183 (2008)  -  DOI: https://doi.org/10.3354/ame01209

ABSTRACT: Rates of dinitrogen (N₂) fixation were measured at Stn ALOHA in the North Pacific Subtropical Gyre (NPSG) on 9 cruises during the period April 2004 to March 2005. On each cruise, a near-surface (5 m) seawater sample was incubated with ¹⁵N-labeled N₂ under simulated in situ conditions for 24 h prior to filtration of either whole water or <10 µm filtrate on microfine (0.7 µm nominal porosity) glass fiber filters; on 3 cruises, surface to 125 m depth profiles of size-fractionated N₂ fixation rates were also obtained. Nearly all (on average 95%) of the net N₂ fixation in the euphotic zone occurred in the upper 75 m, and was mostly (64 ± 5 [SE]%) contained in the <10 µm size fraction following a 24 h incubation period. Highest surface diazotroph activity at this site was observed in July to August (1.63 to 1.68 µmol N m^–3 d^–1) and lowest N₂ fixation rates occurred in September to November (0.38 to 0.68 µmol N m^–3 d^–1). Vertically integrated rates of whole community N₂ fixation (measured in November, February and March) varied 5-fold (20.2 to 109 µmol N m^–2 d^–1). The short-term response of the microbial community to the addition of iron (Fe) and/or phosphorus (P) was variable, suggesting that contemporaneous N₂ fixation at Stn ALOHA may be controlled by the population dynamics of the various diazotroph species rather than by instantaneous resource limitation.

KEY WORDS: Nitrogen fixation · Diazotroph · Stn ALOHA · North Pacific gyre

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Cite this article as: Grabowski MNW, Church MJ, Karl DM (2008) Nitrogen fixation rates and controls at Stn ALOHA. Aquat Microb Ecol 52:175-183. https://doi.org/10.3354/ame01209 Export citation Share:    Facebook - - linkedIn