Revisiting the distribution of oceanic N2 fixation and estimating diazotrophic contribution to marine production

Tang, Wanhu; Wang, Seaver; Fonseca-Batista, Debany; Dehairs, Frank; Gifford, Scott M.; González, Aridane G.; Gallinari, Morgane; Planquette, Hélène; Sarthou, Géraldine; Cassar, Nicolas

doi:10.1038/s41467-019-08640-0

Cited by 77 publications

(100 citation statements)

References 93 publications

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“…Our observation of high rates (>500 μmol N·m −2 ·day −1 ) at inshore stations supports the growing body of evidence that ocean margins contribute a greater amount of newly fixed N than previously thought Tang et al, 2019). Our observation of high rates (>500 μmol N·m −2 ·day −1 ) at inshore stations supports the growing body of evidence that ocean margins contribute a greater amount of newly fixed N than previously thought Tang et al, 2019).…”

Section: Discussionsupporting

confidence: 85%

Dinitrogen Fixation Across Physico‐Chemical Gradients of the Eastern Tropical North Pacific Oxygen Deficient Zone

Selden

Mulholland

Bernhardt

et al. 2019

Global Biogeochemical Cycles

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The Eastern Tropical North Pacific Ocean hosts one of the world's largest oceanic oxygen deficient zones (ODZs). Hot spots for reactive nitrogen (Nr) removal processes, ODZs generate conditions proposed to promote Nr inputs via dinitrogen (N2) fixation. In this study, we quantified N2 fixation rates by 15N tracer bioassay across oxygen, nutrient, and light gradients within and adjacent to the ODZ. Within subeuphotic oxygen‐deplete waters, N2 fixation was largely undetectable; however, addition of dissolved organic carbon stimulated N2 fixation in suboxic (<20 μmol/kg O2) waters, suggesting that diazotroph communities are likely energy limited or carbon limited and able to fix N2 despite high ambient concentrations of dissolved inorganic nitrogen. Elevated rates (>9 nmol N·L−1·day−1) were also observed in suboxic waters near volcanic islands where N2 fixation was quantifiable to 3,000 m. Within the overlying euphotic waters, N2 fixation rates were highest near the continent, exceeding 500 μmol N·m−2·day−1 at one third of inshore stations. These findings support the expansion of the known range of diazotrophs to deep, cold, and dissolved inorganic nitrogen‐replete waters. Additionally, this work bolsters calls for the reconsideration of ocean margins as important sources of Nr. Despite high rates at some inshore stations, regional N2 fixation appears insufficient to compensate for Nr loss locally as observed previously in the Eastern Tropical South Pacific ODZ.

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Section: Discussionsupporting

confidence: 85%

Dinitrogen Fixation Across Physico‐Chemical Gradients of the Eastern Tropical North Pacific Oxygen Deficient Zone

Selden

Mulholland

Bernhardt

et al. 2019

Global Biogeochemical Cycles

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“…Richelia shows a relatively homogeneous distribution in the tropical ocean with hot spots predicted in the Amazon River plume, near Hawaii, and in the Mediterranean Sea, in agreement with observations from studies not included in our training dataset (Crombet et al, 2011;Villareal et al, 2012;Weber et al, 2016). In addition, although the quantification of diazotrophs in coastal oceans is scarce in our dataset, diazotrophic hot spots are predicted in coastal waters (e.g., eastern American coast, coast of islands in the western Pacific), in line with the recent studies of Tang, Wang, et al (2019) and Mulholland et al (2019). More broadly, the RF-estimated distributions of diazotrophs combining Trichodesmium, UCYN-A, UCYN-B, and Richelia match the modeled distribution of N 2 fixation by Tang, Li, and Cassar (2019).…”

Section: Machine Learning Estimates and Comparison To Other Model Simsupporting

confidence: 91%

“…Most models generally restrict diazotrophs to the oligotrophic tropical and subtropical surface waters. However, this classic paradigm is increasingly being challenged by observations of diazotrophs in aphotic, polar, and coastal waters (Bonnet et al, ; Harding et al, ; Tang, Wang, et al, ). Our RF model indeed predicts high abundance of diazotrophs in the undersampled coastal waters, South Atlantic, southern Indian Ocean, and polar regions.…”

Section: Resultsmentioning

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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“…Richelia symbioses inside the cells of several host diatoms, such as Rhizosolenia/Guinardia and Hemiaulus, whereas Calothrix attaches epiphytically to host diatoms, such as Chaetoceros and Bacteriastrum (Gómez et al, 2005;Tuo et al, 2014Tuo et al, , 2017Venrick, 1974;Villareal, 1992). Recent studies have shown unicellular cyanobacteria and noncyanobacterial diazotrophs (particularly proteobacteria) to be more widespread and actively N 2 fixing in the marine environments than previously thought (Li et al, 2019;Moisander et al, 2010;Tang et al, 2019;Zehr et al, 2001). However, it appears that the filamentous Trichodesmium and Richelia/Calothrix remain to be crucial N 2 -fixing cyanobacteria throughout the warm oligotrophic ocean (Capone et al, 1997(Capone et al, , 2005Carpenter et al, 1999;Foster et al, 2011;Zehr, 2011).…”

Section: Introductionmentioning

confidence: 98%

“…Therefore, Kuroshio and its branches strongly intrude into the ECS and SYS (ECSYS), which profoundly influence the physicochemical environment and biogeochemical processes (Chen, 2009;Zhang et al, 2007). N 2 fixation rates (NFRs) in Kuroshio and adjacent waters Shiozaki et al, 2010;Wu et al, 2018;Zhang et al, 2012) were found to be higher than those reported in most global seas (Landolfi et al, 2018;Luo et al, 2012;Tang et al, 2019). Kuroshio is recognized as the hotspot of N 2 fixation in the Pacific Ocean where fixed N contributes significant role in the N budget (Shiozaki et al, 2010;Shiozaki, Takeda, et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Kuroshio Shape Composition and Distribution of Filamentous Diazotrophs in the East China Sea and Southern Yellow Sea

et al. 2019

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The filamentous Trichodesmium and Richelia/Calothrix appear to be crucial N 2 -fixing cyanobacteria throughout the warm oligotrophic ocean, particularly in western boundary currents. The Kuroshio, the hotspot of N 2 fixation in the Pacific Ocean, intrudes into the East China Sea (ECS) and southern Yellow Sea (SYS), which may profoundly influence composition and distribution of filamentous diazotrophs. We provide high spatial resolution dataset of filamentous diazotrophs in the ECS and SYS in July and August 2013. Results showed that Trichodesmium colonies and Richelia/Calothrix were strictly restricted to warm, saline, nitrogen-limited waters of the ECS influenced by Kuroshio and were not detected in the SYS. The density of Trichodesmium in the ECS and SYS was 8.48 × 10 6 trichomes/m 2 , and colonial trichomes accounted for 40%. In addition to free filaments, Richelia/Calothrix were found to be symbiotic with diatoms Hemiaulus, Rhizosolenia/Guinardia, Chaetoceros, and Bacteriastrum with a total density at 2.13 × 10 6 heterocysts/m 2 in the ECS. The densities of filamentous diazotrophs were significantly higher in high-salinity region of the ECS (mainly controlled by Kuroshio) than in low-salinity region of the ECS and in the SYS. The densities of Trichodesmium and Richelia/Calothrix were significantly and positively correlated with temperature, salinity, and mixed-layer depth but were negatively correlated with NO 3 , turbidity, and chlorophyll-a. These results suggested that composition and distribution of filamentous diazotrophs in the ECS and SYS were largely shaped by Kuroshio and associated physicochemical properties. We hypothesize that active N 2 fixation in Kuroshio may be substantially supported by Richelia/Calothrix in addition to Trichodesmium.

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Revisiting the distribution of oceanic N2 fixation and estimating diazotrophic contribution to marine production

Cited by 77 publications

References 93 publications

Dinitrogen Fixation Across Physico‐Chemical Gradients of the Eastern Tropical North Pacific Oxygen Deficient Zone

Dinitrogen Fixation Across Physico‐Chemical Gradients of the Eastern Tropical North Pacific Oxygen Deficient Zone

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

Kuroshio Shape Composition and Distribution of Filamentous Diazotrophs in the East China Sea and Southern Yellow Sea

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