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Diversity trumps acidification : lack of evidence for carbon dioxide enhancement of Trichodesmium community nitrogen or carbon fixation at Station ALOHA

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  • We conducted 11 independent short-term carbon dioxide (CO₂) manipulation experiments using colonies of the filamentous cyanobacteria Trichodesmium isolated on three cruises in the North Pacific Subtropical Gyre (NPSG). Dinitrogen (N₂) and carbon (C) fixation rates of these colonies were compared over CO₂ conditions ranging from ~ 18 Pa (equivalent to last glacial maximum atmospheric P[subscript CO₂]) to ~ 160 Pa (predicted for ~ year 2200). Our results indicate that elevated P[subscript CO₂] has no consistent significant effect on rates of N₂ or C fixation by Trichodesmium colonies in the NPSG under present environmental conditions. Differences between P[subscript CO₂] treatments were not modulated by phosphorus amendments, iron amendments, or light level. Sequencing the hetR, nifH, 16S, and internal transcribed spacer genes of Trichodesmium colonies revealed a highly diverse community of Trichodesmium and other N₂-fixing colony-associated organisms. The species composition of Trichodesmium demonstrated spatiotemporal variability, but over half of total sequences were phylogenetically closely related (> 99% hetR sequence similarity) to isolate H9-4 of T. erythraeum, which showed no response to elevated P[subscript CO₂] in previous laboratory experiments. Our handpicked Trichodesmium colonies included a substantial number of organisms other than Trichodesmium with the metabolic capacity for N₂ and C fixation. We suggest that the diverse assemblage of Trichodesmium species and coexisting microorganisms within the colonies can explain the lack of an observed CO₂ enhancement of N₂ or C fixation rates, because different species are known to have different specific affinities for CO₂.
  • This is the publisher’s final pdf. The published article is copyrighted by the Association for the Sciences of Limnology and Oceanography, Inc. and can be found at: http://aslo.org/lo/.
  • Keywords: Diazotroph Trichodesmium, N-2 fixation, Marine Cyanobacterium Trichodesmium
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  • Gradoville, M. R., White, A. E., Böttjer, D., Church, M. J., & Letelier, R. M. (2014). Diversity trumps acidification: Lack of evidence for carbon dioxide enhancement of Trichodesmium community nitrogen or carbon fixation at Station ALOHA. Limnology and Oceanography, 59(3), 645-659. doi:10.4319/lo.2014.59.3.0645
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  • 59
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  • 3
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  • Support for this project was provided by the National Science Foundation (OCE 08-50827 to RML and MJC).
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