Aphotic N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fixation along an oligotrophic to ultraoligotrophic transect in the Western Tropical South Pacific Ocean

Benavides, Mar; Shoemaker, Katyanne M.; Moisander, Pia H.; Niggemann, Jutta; Dittmar, Thorsten; Duhamel, Solange; Grosso, Olivier; Pujo‐Pay, Mireille; Hélias-Nunige, Sandra

doi:10.5194/bg-2017-542

Cited by 3 publications

(3 citation statements)

References 38 publications

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“…Luo et al () assembled 109 and 921 observations of depth‐integrated and volumetric diazotroph abundances, respectively, as estimated by quantitative polymerase chain reaction (qPCR) assays targeting the nifH genes of various diazotrophs including Trichodesmium , UCYN‐A1, UCYN‐A2, UCYN‐B, UCYN‐C, Richelia , Calothrix , and some noncyanobacterial diazotrophs. Since publication of the database, the number of observations has rapidly expanded, with new data collected in coastal, aphotic, and polar waters (Benavides et al, ; Shiozaki, Fujiwara, et al, ; Tang, Wang, et al, ). In light of such progress, updating the Luo et al () database of diazotroph abundances and reevaluating the environmental controls on their distributions in the world's oceans represents a timely effort.…”

Section: Introductionmentioning

confidence: 99%

Data‐Driven Modeling of the Distribution of Diazotrophs in the Global Ocean

Tang

Cassar

2019

Geophysical Research Letters

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Diazotrophs play a critical role in the biogeochemical cycling of nitrogen, carbon, and other elements in the global ocean. Despite their well‐recognized role, the diversity, abundance, and distribution of diazotrophs in the world's ocean remain poorly characterized largely due to limited observations. Here we update the database of diazotroph nifH gene abundances and assess how environmental factors may regulate diazotrophs at the global scale. Our meta‐analysis more than doubles the number of observations in the previous database. Using linear and nonlinear regressions, we find that the abundances of Trichodesmium, UCYN‐A, UCYN‐B, and Richelia relate differently to temperature, light, and nutrients. We further apply a random forest algorithm to estimate the global distributions of these diazotrophic groups, identifying undersampled potential hot spots of diazotrophy in the South Atlantic and southern Indian Ocean, and in coastal waters. The distinct ecophysiologies of diazotrophs highlighted here argue for separate parameterizations of different diazotrophs in model simulations.

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Section: Introductionmentioning

confidence: 99%

Data‐Driven Modeling of the Distribution of Diazotrophs in the Global Ocean

Tang

Cassar

2019

Geophysical Research Letters

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“…It has been widely assumed that marine N 2 fixation is inhibited by the presence of nitrate, however, recent discoveries of diazotrophs and measurements of N 2 fixation rates in nitrate-replete marine environments such as coastal systems ( Mulholland et al, 2012 ; Thompson et al, 2014 ), regions with seasonal upwelling ( Sohm et al, 2011a ; Moreira-Coello et al, 2017 ), mesopelagic waters ( Hamersley et al, 2011 ; Benavides et al, 2018 ), the Bering ( Shiozaki et al, 2017 ) and Chukchi Seas ( Shiozaki et al, 2018 ) in the Arctic, the Great Belt ( Bentzon-Tilia et al, 2015 ) and oxygen minimum zones ( Fernandez et al, 2011 ), suggests that the influence of DIN availability on diazotroph biogeography and N 2 fixation is not well-understood. The assumption that DIN inhibits N 2 fixation is based on several lines of evidence including the competitive disadvantage faced by diazotrophs due to the energetic tradeoff between N 2 fixation verses nitrate assimilation ( Falkowski, 1997 ), early observations of Trichodesmium only in N-depleted surface waters of the oligotrophic ocean ( Capone et al, 1997 ), and direct measurements of nitrate and/or ammonia inhibition of N 2 fixation in culture experiments (e.g., Mulholland and Capone, 1999 ; Holl and Montoya, 2005 ).…”

Section: Introductionmentioning

confidence: 99%

In Situ Diazotroph Population Dynamics Under Different Resource Ratios in the North Pacific Subtropical Gyre

et al. 2018

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Major advances in understanding the diversity, distribution, and activity of marine N2-fixing microorganisms (diazotrophs) have been made in the past decades, however, large gaps in knowledge remain about the environmental controls on growth and mortality rates. In order to measure diazotroph net growth rates and microzooplankton grazing rates on diazotrophs, nutrient perturbation experiments and dilution grazing experiments were conducted using free-floating in situ incubation arrays in the vicinity of Station ALOHA in March 2016. Net growth rates for targeted diazotroph taxa as well as Prochlorococcus, Synechococcus and photosynthetic picoeukaryotes were determined under high (H) and low (L) nitrate:phosphate (NP) ratio conditions at four depths in the photic zone (25, 45, 75, and 100 m) using quantitative PCR and flow cytometry. Changes in the prokaryote community composition in response to HNP and LNP treatments were characterized using 16S rRNA variable region tag sequencing. Microzooplankton grazing rates on diazotrophs were measured using a modified dilution technique at two depths in the photic zone (15 and 125 m). Net growth rates for most of the targeted diazotrophs after 48 h were not stimulated as expected by LNP conditions, rather enhanced growth rates were often measured in HNP treatments. Interestingly, net growth rates of the uncultivated prymnesiophyte symbiont UCYN-A1 were stimulated in HNP treatments at 75 and 100 m, suggesting that N used for growth was acquired through continuing to fix N2 in the presence of nitrate. Net growth rates for UCYN-A1, UCYN-C, Crocosphaera sp. (UCYN-B) and the diatom symbiont Richelia (associated with Rhizosolenia) were uniformly high at 45 m (up to 1.6 ± 0.5 d-1), implying that all were growing optimally at the onset of the experiment at that depth. Differences in microzooplankton grazing rates on UCYN-A1 and UCYN-C in 15 m waters indicate that the grazer assemblage preyed preferentially on UCYN-A1. Deeper in the water column (125 m), both diazotrophs were grazed at substantial rates, suggesting grazing pressure may increase with depth in the photic zone. Constraining in situ diazotroph growth and mortality rates are important steps for improving parameterization for diazotrophs in global ecosystem models.

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“…However, sequencing of the nitrogenase (nifH) gene has revealed unicellular cyanobacterial and diverse noncyanobacterial marine diazotrophs with broad geographic ranges (Zehr et al 1998;Moisander et al 2010;Farnelid et al 2011). Furthermore, recent surveys have reported diazotrophic genes and/or N 2 fixation rates (NFRs) in unexpected environments, including high-nutrient coastal systems (Mulholland et al 2012;Bentzon-Tilia et al 2015), oxygen minimum zones (Loescher et al 2014;Jayakumar et al 2017), polar regions (Blais et al 2012;Harding et al 2018;, and the deep sea (Hewson et al 2007;Benavides et al 2018). Thus, the biogeography and environmental controls of marine diazotrophs are still not well understood.…”

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confidence: 99%

Latitudinal constraints on the abundance and activity of the cyanobacterium UCYN‐A and other marine diazotrophs in the North Pacific

Gradoville

Farnelid

White

et al. 2020

Limnology & Oceanography

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The number of marine environments known to harbor dinitrogen (N 2)-fixing (diazotrophic) microorganisms is increasing, prompting a reassessment of the biogeography of marine diazotrophs and N 2 fixation rates (NFRs). Here, we investigate the diversity, abundance, and activity of diazotrophic microorganisms in the North Pacific Subtropical Gyre (NPSG), a diazotrophic habitat, and the North Pacific Transition Zone (NPTZ), a region characterized by strong physical, chemical, and biological gradients. Samples were collected on two springtime meridional cruises during 2016 and 2017, spanning from 23.5 N to 41.4 N along 158 W. We observed an abrupt decrease in diazotrophic abundances near the southern edge of the NPTZ, which coincided with a salinity front and with a $10-fold increase in Synechococcus abundance, but without a concomitant change in phosphate or nitrate concentrations. In NPSG waters south of this diazotrophic boundary, nifH genes and NFRs were consistently detected and diazotrophic communities were dominated by UCYN-A, an uncultivated, symbiotic cyanobacterium (2.8 × 10 3 to 1.0 × 10 6 nifH gene copies L −1). There was a significant positive relationship between quantitative polymerase chain reaction-derived UCYN-A nifH gene abundances and community NFRs in the NPSG, suggesting a large contribution of UCYN-A to community NFRs. In the NPTZ waters to the north, NFRs were low or undetected and nifH genes were rare, with the few detected sequences represented by UCYN-A and noncyanobacterial diazotrophs. The patterns we observed in UCYN-A abundance in the context of local biogeochemistry suggest that the environmental controls of this organism may differ from those of cultivated marine cyanobacterial diazotrophs.

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Aphotic N<sub>2</sub> fixation along an oligotrophic to ultraoligotrophic transect in the Western Tropical South Pacific Ocean

Cited by 3 publications

References 38 publications

Data‐Driven Modeling of the Distribution of Diazotrophs in the Global Ocean

Data‐Driven Modeling of the Distribution of Diazotrophs in the Global Ocean

In Situ Diazotroph Population Dynamics Under Different Resource Ratios in the North Pacific Subtropical Gyre

Latitudinal constraints on the abundance and activity of the cyanobacterium UCYN‐A and other marine diazotrophs in the North Pacific

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