Assessment of the dinitrogen released as ammonium and dissolved organic nitrogen by unicellular and filamentous marine diazotrophic cyanobacteria grown in culture

Berthelot, Hugo; Bonnet, Sophie; Camps, Mercedes; Grosso, Olivier; Moutin, Thierry

doi:10.3389/fmars.2015.00080

Cited by 50 publications

(89 citation statements)

References 94 publications

(136 reference statements)

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“…5). The overall range agrees well with previous field studies (Glibert and Bronk, 1994;Mulholland et al, 2006;Bonnet et al, 2016a;Konno et al, 2010;Benavides et al, 2013;Berthelot et al, 2015). Our data revealed that the fraction of DDN release to gross NF increased as light decreased (all p values < 0.05).…”

Section: Ddn Net Release To the Dissolved Poolsupporting

confidence: 92%

“…In fact, in unialgal culture experiments (Berthelot et al, 2015), CF : NF ratios (1.8-5.6) were quite close to the POC : PON ratio (3.8-5.5) of a variety of diazotrophs including Trichodesmium. In our field study, the abundance of Trichodesmium was up to 4227 trichomes L −1 , and the measured CF : NF ratios (9.3) at in situ light were close to the initial POC : PON ratio (6.4).…”

Section: Metabolism Tradeoff Between Carbon and Nitrogen Fixation Undmentioning

confidence: 59%

“…At station A0320 high light intensities (> 400 µE m −2 s −1 ), the final POC and PON concentrations increased significantly, also implying an active physiology status of Trichodesmium, and the fraction of DD 15 N release in the dissolved pool ranged from 6 % ± 6 % to 23 % ± 5 %. Actually, several unialgal culture studies, including Trichodesmium and UCYN-B and UCYN-C, showed less than 2 % DD 15 N release in the dissolved pool (Berthelot et al, 2015;Benavides et al, 2013). These low values were attributable to the exponential growth phase and optimal growth conditions and a lack of exogenous factor influence such as viral lysis (Hewson et al, 2004) and sloppy feeding (O'Neil et al, 1996).…”

Section: Light Modulation Of Ddn Net Release Fractionmentioning

confidence: 99%

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Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

et al. 2018

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Abstract. Dinitrogen fixation (NF) by marine cyanobacteria is an important pathway to replenish the oceanic bioavailable nitrogen inventory. Light is the key to modulating NF; however, field studies investigating the light response curve (NF-I curve) of NF rate and the effect of light on diazotrophderived nitrogen (DDN) net release are relatively sparse in the literature, hampering prediction using models. A dissolution method was applied using uncontaminated 15 N 2 gas to examine how the light changes may influence the NF intensity and DDN net release in the oligotrophic ocean. Experiments were conducted at stations with diazotrophs dominated by filamentous cyanobacterium Trichodesmium spp. in the western Pacific and the South China Sea. The effect of light on carbon fixation (CF) was measured in parallel using the 13 C tracer method specifically for a station characterized by Trichodesmium bloom. Both NF-I and CF-I curves showed a I k (light saturation coefficient) range of 193 to 315 µE m −2 s −1 , with light saturation at around 400 µE m −2 s −1 . The proportion of DDN net release ranged from ∼ 6 to ∼ 50 %, suggesting an increasing trend as the light intensity decreased. At the Trichodesmium bloom station, we found that the CF / NF ratio was light-dependent and the ratio started to increase as light was lower than the carbon compensation point of 200 µE m −2 s −1 . Under low-light stress, Trichodesmium physiologically preferred to allocate more energy for CF to alleviate the intensive carbon consumption by respiration; thus, there is a metabolism tradeoff between CF and NF pathways. Results showed that shortterm (< 24 h) light change modulates the physiological state, which subsequently determined the C / N metabolism and DDN net release by Trichodesmium. Reallocation of energy associated with the variation in light intensity would be helpful for prediction of the global biogeochemical cycle of N by models involving Trichodesmium blooms.

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Section: Ddn Net Release To the Dissolved Poolsupporting

confidence: 92%

Section: Metabolism Tradeoff Between Carbon and Nitrogen Fixation Undmentioning

confidence: 59%

Section: Light Modulation Of Ddn Net Release Fractionmentioning

confidence: 99%

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Effect of light on N2 fixation and net nitrogen release of Trichodesmium in a field study

et al. 2018

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“…For example, DDN contribution to the primary production of Red Sea coral rocks varied from 2% in winter to more than 27% in summer, considering the maximal net primary production measured at midday . Moreover, DDN cannot only contribute to support the growth of primary producers, but also the growth of secondary producers via fixed nitrogen release from diazotroph cells (Mulholland et al, 2004;Berthelot et al, 2015;Bonnet et al, 2016), grazing (Williams and Carpenter, 1997), or via diazotroph biomass recycling. The estimations of the annual average of the total contribution of DDN to reef nitrogen cycle thus vary from 150 to ca.…”

Section: Contribution Of N 2 Fixation To Primary Productivitymentioning

confidence: 99%

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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Coral reefs are highly productive ecosystems thriving in nutrient-poor waters. Their productivity depends largely on the availability of nitrogen, the proximate limiting nutrient for primary production. In reefs, the major nitrogen pathways include regeneration, nitrification, ammonification and dinitrogen (N 2 ) fixation. N 2 fixation is performed by prokaryotes called "diazotrophs" that abound in coral rubbles, sandy bottoms, microbial mats, or seagrass meadows. Corals, which are the main reef builders, have developed a partnership with dinoflagellates which transform dissolved inorganic nitrogen into amino acids and protein, and with diazotrophs to gain diazotrophically-derived nitrogen (DDN). Pioneering studies found active diazotrophic cyanobacteria in the corals' mucus and/or tissue, and later high throughput sequencing efforts have described diverse communities of non-cyanobacterial diazotrophs associated with scleractinian corals. Yet, the metabolic processes behind these associations and how they benefit corals are currently not well understood. While genomic studies describe the diversity of diazotrophs and isotopic tracer experiments quantify N 2 fixation rates, combined advanced methods are needed to elucidate the mechanisms behind the transfer of DDN to the coral holobiont and whether these mechanisms change according to the identity of the diazotrophs or coral species. Here we review our current knowledge on N 2 fixation in corals: the diversity and localization of diazotrophs in the coral holobiont, the environmental factors controlling N 2 fixation, the fate of DDN within the coral symbiosis as well as its potential role in coral resilience. We finally summarize the unknowns: are the diversity, abundance and localization of diazotrophs within the holobiont species-and/or site-specific? Do they have an impact on DDN production? What are the metabolic mechanisms implicated? Do they change spatially, temporally or according to environmental factors? We encourage scientists to undertake research efforts to tackle these questions in order to shed light on nitrogen cycling in reef ecosystems and to understand if coral-associated N 2 fixation can improve coral's resilience in the face of climate change.

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“…Dissolved N is released through a combination of endogenous and exogenous processes, including viral lysis (Hewson et al, 2004), zooplankton sloppy feeding (O'Neil et al, 1996), or programmed cell death (Berman-Frank et al, 2004). Recent research has demonstrated that UCYN can release similar amounts of dissolved N to Trichodesmium (Berthelot et al, 2015a).…”

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confidence: 99%

Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

et al. 2016

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Abstract. In oligotrophic tropical and subtropical oceans, where strong stratification can limit the replenishment of surface nitrate, dinitrogen (N 2 ) fixation by diazotrophs can represent a significant source of nitrogen (N) for primary production. The VAHINE (VAriability of vertical and tropHIc transfer of fixed N 2 in the south-wEst Pacific) experiment was designed to examine the fate of diazotroph-derived nitrogen (DDN) in such ecosystems. In austral summer 2013, three large (∼ 50 m 3 ) in situ mesocosms were deployed for 23 days in the New Caledonia lagoon, an ecosystem that typifies the low-nutrient, low-chlorophyll environment, to stimulate diazotroph production. The zooplankton component of the study aimed to measure the incorporation of DDN into zooplankton biomass, and assess the role of direct diazotroph grazing by zooplankton as a DDN uptake pathway. Inside the mesocosms, the diatom-diazotroph association (DDA) het-1 predominated during days 5-15 while the unicellular diazotrophic cyanobacteria UCYN-C predominated during days 15-23. A Trichodesmium bloom was observed in the lagoon (outside the mesocosms) towards the end of the experiment. The zooplankton community was dominated by copepods (63 % of total abundance) for the duration of the experiment. Using two-source N isotope mixing models we estimated a mean ∼ 28 % contribution of DDN to zooplankton nitrogen biomass at the start of the experiment, indicating that the natural summer peak of N 2 fixation in the lagoon was already contributing significantly to the zooplankton. Stimulation of N 2 fixation in the mesocosms corresponded with a generally low-level enhancement of DDN contribution to zooplankton nitrogen biomass, but with a peak of ∼ 73 % in mesocosm 1 following the UCYN-C bloom. qPCR analysis targeting four of the common diazotroph groups present in the mesocosms (Trichodesmium, het-1, het-2, UCYN-C) demonstrated that all four were ingested by copepod grazers, and that their abundance in copepod stomachs generally corresponded with their in situ abundance. 15 N 2 labelled grazing experiments therefore provided evidence for direct ingestion and assimilation of UCYN-C-derived N by the zooplankton, but not for het-1 and Trichodesmium, supporting an important role of secondary pathways of DDN to the zooplankton for the latter groups, i.e. DDN contributions to the dissolved N pool and uptake by nondiazotrophs. This study appears to provide the first evidence of direct UCYN-C grazing by zooplankton, and indicates that UCYN-C-derived N contributesPublished by Copernicus Publications on behalf of the European Geosciences Union.

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Assessment of the dinitrogen released as ammonium and dissolved organic nitrogen by unicellular and filamentous marine diazotrophic cyanobacteria grown in culture

Abstract: Assessment of the dinitrogen released as ammonium and dissolved organic nitrogen by unicellular and filamentous marine diazotrophic cyanobacteria grown in culture. Front. Mar. Sci. 2:80.

Cited by 50 publications

References 94 publications

Effect of light on N<sub>2</sub> fixation and net nitrogen release of <i>Trichodesmium</i> in a field study

Effect of light on N<sub>2</sub> fixation and net nitrogen release of <i>Trichodesmium</i> in a field study

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

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Assessment of the dinitrogen released as ammonium and dissolved organic nitrogen by unicellular and filamentous marine diazotrophic cyanobacteria grown in culture

Abstract: Assessment of the dinitrogen released as ammonium and dissolved organic nitrogen by unicellular and filamentous marine diazotrophic cyanobacteria grown in culture. Front. Mar. Sci. 2:80.

Cited by 50 publications

References 94 publications

Effect of light on N&lt;sub&gt;2&lt;/sub&gt; fixation and net nitrogen release of &lt;i&gt;Trichodesmium&lt;/i&gt; in a field study

Effect of light on N&lt;sub&gt;2&lt;/sub&gt; fixation and net nitrogen release of &lt;i&gt;Trichodesmium&lt;/i&gt; in a field study

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

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Effect of light on N<sub>2</sub> fixation and net nitrogen release of <i>Trichodesmium</i> in a field study

Effect of light on N<sub>2</sub> fixation and net nitrogen release of <i>Trichodesmium</i> in a field study