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Sharpe G, Zhao L, Meyer MG, Gong W, Burns SM, Tagliabue A, Buck KN, Santoro AE, Graff JR, Marchetti A, Gifford S. Synechococcus nitrogen gene loss in iron-limited ocean regions. ISME COMMUNICATIONS 2023; 3:107. [PMID: 37783796 PMCID: PMC10545762 DOI: 10.1038/s43705-023-00314-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 09/15/2023] [Accepted: 09/21/2023] [Indexed: 10/04/2023]
Abstract
Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export.
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Affiliation(s)
- Garrett Sharpe
- Environment Ecology and Energy Program, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Liang Zhao
- Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Meredith G Meyer
- Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Weida Gong
- Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Shannon M Burns
- College of Marine Science, University of South Florida, St. Petersburg, FL, USA
| | | | - Kristen N Buck
- College of Marine Science, University of South Florida, St. Petersburg, FL, USA
- College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
| | - Alyson E Santoro
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, CA, USA
| | - Jason R Graff
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
| | - Adrian Marchetti
- Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Scott Gifford
- Earth, Marine and Environmental Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
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Tagliabue A, Twining BS, Barrier N, Maury O, Berger M, Bopp L. Ocean iron fertilization may amplify climate change pressures on marine animal biomass for limited climate benefit. GLOBAL CHANGE BIOLOGY 2023; 29:5250-5260. [PMID: 37409536 DOI: 10.1111/gcb.16854] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/15/2023] [Accepted: 06/16/2023] [Indexed: 07/07/2023]
Abstract
Climate change scenarios suggest that large-scale carbon dioxide removal (CDR) will be required to maintain global warming below 2°C, leading to renewed attention on ocean iron fertilization (OIF). Previous OIF modelling has found that while carbon export increases, nutrient transport to lower latitude ecosystems declines, resulting in a modest impact on atmospheric CO2 . However, the interaction of these CDR responses with ongoing climate change is unknown. Here, we combine global ocean biogeochemistry and ecosystem models to show that, while stimulating carbon sequestration, OIF may amplify climate-induced declines in tropical ocean productivity and ecosystem biomass under a high-emission scenario, with very limited potential atmospheric CO2 drawdown. The 'biogeochemical fingerprint' of climate change, that leads to depletion of upper ocean major nutrients due to upper ocean stratification, is reinforced by OIF due to greater major nutrient consumption. Our simulations show that reductions in upper trophic level animal biomass in tropical regions due to climate change would be exacerbated by OIF within ~20 years, especially in coastal exclusive economic zones (EEZs), with potential implications for fisheries that underpin the livelihoods and economies of coastal communities. Any fertilization-based CDR should therefore consider its interaction with ongoing climate-driven changes and the ensuing ecosystem impacts in national EEZs.
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Affiliation(s)
| | | | - Nicolas Barrier
- MARBEC, IRD, IFREMER, CNRS, Université de Montpellier, Montpellier, France
| | - Olivier Maury
- MARBEC, IRD, IFREMER, CNRS, Université de Montpellier, Montpellier, France
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Fourquez M, Janssen DJ, Conway TM, Cabanes D, Ellwood MJ, Sieber M, Trimborn S, Hassler C. Chasing iron bioavailability in the Southern Ocean: Insights from Phaeocystis antarctica and iron speciation. SCIENCE ADVANCES 2023; 9:eadf9696. [PMID: 37379397 DOI: 10.1126/sciadv.adf9696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 05/24/2023] [Indexed: 06/30/2023]
Abstract
Dissolved iron (dFe) availability limits the uptake of atmospheric CO2 by the Southern Ocean (SO) biological pump. Hence, any change in bioavailable dFe in this region can directly influence climate. On the basis of Fe uptake experiments with Phaeocystis antarctica, we show that the range of dFe bioavailability in natural samples is wider (<1 to ~200% compared to free inorganic Fe') than previously thought, with higher bioavailability found near glacial sources. The degree of bioavailability varied regardless of in situ dFe concentration and depth, challenging the consensus that sole dFe concentrations can be used to predict Fe uptake in modeling studies. Further, our data suggest a disproportionately major role of biologically mediated ligands and encourage revisiting the role of humic substances in influencing marine Fe biogeochemical cycling in the SO. Last, we describe a linkage between in situ dFe bioavailability and isotopic signatures that, we anticipate, will stimulate future research.
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Affiliation(s)
- Marion Fourquez
- Aix Marseille Univ., Université de Toulon, CNRS, IRD, MIO UMR 110, Marseille 13288, France
- University of Geneva, Department F.-A. Forel for Environmental and Aquatic Sciences, Geneva 1211, Switzerland
| | - David J Janssen
- Department Surface Waters, Eawag-Swiss Federal Institute of Aquatic Science and Technology, Kastanienbaum, Switzerland
| | - Tim M Conway
- College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA
| | - Damien Cabanes
- University of Geneva, Department F.-A. Forel for Environmental and Aquatic Sciences, Geneva 1211, Switzerland
| | - Michael J Ellwood
- Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia
- Australian Centre for Excellence in Antarctic Science, Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia
| | - Matthias Sieber
- College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA
- Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
| | - Scarlett Trimborn
- Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Bremerhaven 27570, Germany
| | - Christel Hassler
- University of Geneva, Department F.-A. Forel for Environmental and Aquatic Sciences, Geneva 1211, Switzerland
- Institute of Earth Sciences, University of Lausanne, Lausanne 1015, Switzerland
- School of Architecture, Civil, and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Sion 1951, Switzerland
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Lory C, Van Wambeke F, Fourquez M, Barani A, Guieu C, Tilliette C, Marie D, Nunige S, Berman-Frank I, Bonnet S. Assessing the contribution of diazotrophs to microbial Fe uptake using a group specific approach in the Western Tropical South Pacific Ocean. ISME COMMUNICATIONS 2022; 2:41. [PMID: 37938297 PMCID: PMC9723570 DOI: 10.1038/s43705-022-00122-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 03/26/2022] [Accepted: 04/07/2022] [Indexed: 04/27/2023]
Abstract
Diazotrophs are often limited by iron (Fe) availability in the oligotrophic ocean. The Western Tropical South Pacific (WTSP) ocean has been suggested as an intense N2 fixation area due to Fe fertilizations through shallow hydrothermal activity. Yet, the Fe demand of diazotrophs in their natural habitat, where they cohabit with other microbial organisms also requiring Fe, remains unknown. Here we develop and apply a method consisting of coupling 55Fe uptake experiments with cell-sorting by flow cytometry, and provide group-specific rates of in situ Fe uptake by the microbial community in the WTSP, in addition to bulk and size fractionation rates. We reveal that the diazotrophs Crocosphaera watsonii and Trichodesmium contribute substantially to the bulk in situ Fe uptake (~33% on average over the studied area), despite being numerically less abundant compared to the rest of the planktonic community. Trichodesmium had the highest cell-specific Fe uptake rates, followed by C. watsonii, picoeukaryotes, Prochlorococcus, Synechococcus and finally heterotrophic bacteria. Calculated Fe:C quotas were higher (by 2 to 52-fold) for both studied diazotrophs compared to those of the non-diazotrophic plankton, reflecting their high intrinsic Fe demand. This translates into a diazotroph biogeographical distribution that appears to be influenced by ambient dissolved Fe concentrations in the WTSP. Despite having low cell-specific uptake rates, Prochlorococcus and heterotrophic bacteria were largely the main contributors to the bulk Fe uptake (~23% and ~12%, respectively). Overall, this group-specific approach increases our ability to examine the ecophysiological role of functional groups, including those of less abundant and/or less active microbes.
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Affiliation(s)
- C Lory
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France.
| | - F Van Wambeke
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
| | - M Fourquez
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
| | - A Barani
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
| | - C Guieu
- Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, LOV, F-06230, Villefranche-sur-Mer, France
| | - C Tilliette
- Sorbonne Université, CNRS, Laboratoire d'Océanographie de Villefranche, LOV, F-06230, Villefranche-sur-Mer, France
| | - D Marie
- Sorbonne Université, CNRS, Station Biologique de Roscoff, Roscoff, France
| | - S Nunige
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
| | - I Berman-Frank
- Department of Marine Biology, The Leon H. Charney School of Marine Sciences, University of Haifa, Haifa, Israel
| | - S Bonnet
- Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France.
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