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Marine Ecology Progress Series

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MEPS 621:33-50 (2019)  -  DOI:

Effects of iron and light availability on phytoplankton photosynthetic properties in the Ross Sea

Anne-Carlijn Alderkamp1,2, Gert L. van Dijken1, Kate E. Lowry1, Kate M. Lewis1, Hannah L. Joy-Warren1, Willem van de Poll3, Patrick Laan4, Loes Gerringa4, Tom O. Delmont5,7, Bethany D. Jenkins6, Kevin R. Arrigo1,*

1Department of Earth System Science, Stanford University, Stanford, CA 94305, USA
2Biology Department, Foothill College, Los Altos Hills, CA 94022, USA
3Department of Ocean Ecosystems, University of Groningen, PO Box 11103, 9700 CC, Groningen, The Netherlands
4Royal Netherlands Institute for Sea Research, OCS, University of Utrecht, PO Box 59, 1790 AB, Den Burg, The Netherlands
5Department of Medicine, University of Chicago, Chicago, IL 60637, USA
6Department of Cell and Molecular Biology and Graduate School of Oceanography, University of Rhode Island, Kingston, RI 02881, USA
7Present address: Génomique Métabolique, Genoscope, Institut François Jacob, CEA, CNRS, 91000 Evry, France
*Corresponding author:

ABSTRACT: Waters of the Southern Ocean are characterized by high macronutrient concentrations but limited availability of trace metals and light, often making it difficult for phytoplankton to achieve maximum growth rates. One strategy employed by Southern Ocean phytoplankton in culture to cope with low light and low dissolved iron (DFe) is to enhance light absorption by increasing their antenna size rather than the number of reaction centers, thereby reducing their Fe demand. Here we provide physiological evidence that natural populations of Southern Ocean phytoplankton employ a similar photoacclimation strategy to cope with low ambient DFe concentrations. During a research cruise to the Ross Sea in 2013-2014, we conducted 4 bioassay experiments in which we manipulated light and DFe concentrations and measured changes in phytoplankton biomass, growth rate, photosynthetic parameters, fluorescence parameters, and pigment composition. Phytoplankton responded strongly to DFe additions, exhibiting significantly higher biomass, growth rates, and photosynthetic competency. At low light, the maximum photosynthetic rate (P*max) was significantly reduced and the photosynthetic efficiency (α*) was unchanged compared to the high light treatment, regardless of phytoplankton species composition or DFe concentration. Our data suggest that Southern Ocean phytoplankton have evolved an Fe-saving strategy whereby they photoacclimate to low light by increasing their photosynthetic unit size, rather than photosynthetic unit number, even when DFe is available. It appears this Fe-saving strategy is characteristic of both Phaeocystis antarctica and diatoms, suggesting that it is a common adaptation among phytoplankton taxa that grow under Fe limitation in the Southern Ocean.

KEY WORDS: Phytoplankton · Photophysiology · Iron limitation · Ross Sea

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Cite this article as: Alderkamp AC, van Dijken GL, Lowry KE, Lewis KM and others (2019) Effects of iron and light availability on phytoplankton photosynthetic properties in the Ross Sea. Mar Ecol Prog Ser 621:33-50.

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