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Taxon-specific response of marine nitrogen fixers to elevated carbon dioxide concentrations

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Much of the bioavailable nitrogen that supports open ocean food webs and biogeochemical cycles is fixed from the atmosphere by marine cyanobacteria of the genera Trichodesmium and Crocosphaera. In previous experiments carried out with a limited set of cyanobacterial isolates, rates of cyanobacterial nitrogen fixation were shown to increase with carbon dioxide concentrations. Here, we report results from a series of laboratory experiments in which we grew seven strains of Trichodesmium and Crocosphaera from the Atlantic and Pacific oceans under a wide range of carbon dioxide concentrations, and monitored rates of nitrogen fixation and growth. We document large, strain-specific differences in the relationship between nitrogen fixation and carbon dioxide concentration, suggesting that individual strains within each genus are adapted to grow and fix nitrogen at different concentrations of carbon dioxide. We apply kinetic constants from the individual carbon dioxide response curves to an illustrative biogeochemical model of the ocean in 2100, which suggests that strains adapted to high carbon dioxide concentrations could potentially be favoured in a future acidified ocean. We suggest that surface ocean carbon dioxide concentrations could constitute a previously unrecognized selective force that shapes the community composition and diversity of nitrogen-fixing cyanobacteria.

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Figure 1: N2 fixation rate response curves as a function of CO2 for seven Trichodesmium and Crocosphaera isolates.
Figure 2: Plots of growth rates versus N2-fixation rates for all cyanobacteria isolates and treatments.
Figure 3: Illustrative model of theoretical N2 fixation rate increases from the present to the year 2100 for four cyanobacteria isolates across their potential global ranges.

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  • 16 July 2013

    In the version of this Letter originally published online, the published online date was incorrect; it should have read 1 July 2013. This has been corrected in all versions of the Letter.


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Support was provided by US National Science Foundation grants OCE 0825319, 0942379, 117030687 and 1260490 to D.A.H., E.A.W. and F-X.F. We thank J. Waterbury for providing access to culture isolates.

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D.A.H. and F-X.F. conceived, designed and carried out the experiments using cultures isolated and maintained by E.A.W. A.T. conceived, designed and performed the computer simulations. N.W. assisted with the work, analysed data, and performed statistical tests. All authors discussed the results and wrote the manuscript.

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Correspondence to David A. Hutchins.

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The authors declare no competing financial interests.

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Hutchins, D., Fu, FX., Webb, E. et al. Taxon-specific response of marine nitrogen fixers to elevated carbon dioxide concentrations. Nature Geosci 6, 790–795 (2013).

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