Nitrogen fixation rates and controls at Stn ALOHA

Abstract

Rates of dinitrogen (N 2 ) 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 15 N-labeled N 2 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 N 2 fixation rates were also obtained. Nearly all (on average 95%) of the net N 2 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 ). The short-term response of the microbial community to the addition of iron (Fe) and/or phosphorus (P) was variable, suggesting that contemporaneous N 2 fixation at Stn ALOHA may be controlled by the population dynamics of the various diazotroph species rather than by instantaneous resource limitation.

A microarray for assessing transcription from pelagic marine microbial taxa

“…were 8 and 11 times, respectively, more abundant in Fe-amended versus P-amended samples. This high increase in cell abundances in response to Fe and low response to P is consistent with previously reported variability in responses of diazotrophs to P and Fe availability in the NPSG Grabowski et al, 2008;Watkins-Brandt et al, 2011). Supplementary Table S1.…”

“…The physics, chemistry and biology of this region is well characterized (Karl and Lukas, 1996;White et al, 2007), and its microbial metagenome is well represented in the nt sequence databases (DeLong et al, 2006;Frias-Lopez et al, 2008;Hewson et al, 2010). In the North Pacific, where N 2 fixation is a major supply of nitrogen (Karl et al, 1997), phosphorus and iron can be the limiting nutrients for N 2 fixation and primary production (Karl et al, 2001;Moore et al, 2006;Grabowski et al, 2008;Karl and Letelier, 2008;Watkins-Brandt et al, 2011). We hypothesized that if microbial taxa were Fe limited, Fe addition would result in decreased transcription of ironstress genes and increased transcription of genes for energy, carbon and nitrogen metabolism.…”

Nitrogen fixation and nitrogenase (nifH) expression in tropical waters of the eastern North Atlantic

“…Although rates of similar magnitude have been reported in the Eastern Mediterranean (5.3 nmolN l À1 h À1 ) (Rees et al, 2006), BNF rates at Stations A and B are relatively high in comparison to rates from the North Pacific (a region where Fe and P may also be limiting or co-limiting), which are generally less than 1.9 nmolN l À1 h À1 (Montoya et al, 2004;Zehr et al, 2007;Fong et al, 2008;Grabowski et al, 2008). Stations C-F had rates o1 nmolN l À1 h À1 , which are comparable to rates reported in Fe-and P-amended waters 800 km south of Station C by Mills et al (2004) and the temperate coastal waters of the English Channel (Rees et al, 2009).…”

Nitrogen fixation within the water column associated with two hypoxic basins in the Southern California Bight

“…Clusters (I, II,and IV) and sub-clusters (1A, 1B, 3K, and 3E), according to nifH-based phylogeny, are shown to the right of the tree. Reference amino acid sequences are followed by GenBank accession nos studies, ranged from 3 to 64% (Dore et al 2002, Falcón et al 2004, Grabowski et al 2008. However, in the eastern temperate North Pacific, at the same latitude as our coastal site but in the open ocean, nanoplankton were responsible for nearly 100% of the measured N 2 fixation (Needoba et al 2007).…”