BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-11-5795-2014 Taxon-specific responses of Southern Ocean diatoms to Fe enrichment revealed by synchrotron radiation FTIR microspectroscopy Sackett O. 1 2 3 Armand L. 4 Beardall J. https://orcid.org/0000-0001-7684-446X 2 Hill R. 5 Doblin M. 1 Connelly C. 6 Howes J. 1 Stuart B. 7 Ralph P. 1 Heraud P. 2 3 Plant Functional Biology and Climate Change Cluster (C3), University of Technology, Sydney, New South Wales, Australia School of Biological Sciences, Monash University, Victoria, Australia Centre for Biospectroscopy, School of Chemistry, Monash University, Victoria, Australia Department of Biological Sciences and Climate Futures, Macquarie University, New South Wales, Australia Centre for Marine Bio-Innovation, University of New South Wales, New South Wales, Australia School of Life and Environmental Sciences, Deakin University, Victoria, Australia School of Chemistry, University of Technology, Sydney, New South Wales, Australia 20 10 2014 11 20 5795 5808 Copyright: © 2014 O. Sackett et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/11/5795/2014/bg-11-5795-2014.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/11/5795/2014/bg-11-5795-2014.pdf

Photosynthesis by marine diatoms contributes substantially to global biogeochemical cycling and ecosystem productivity. It is widely accepted that diatoms are extremely sensitive to changes in Fe availability, with numerous in situ experiments demonstrating rapid growth and increased export of elements (e.g. C, Si and Fe) from surface waters as a result of Fe addition. Less is known about the effects of Fe enrichment on the phenotypes of diatoms, such as associated changes in nutritional value – furthermore, data on taxon-specific responses are almost non-existent. Enhanced supply of nutrient-rich waters along the coast of the subantarctic Kerguelen Island provide a valuable opportunity to examine the responses of phytoplankton to natural Fe enrichment. Here we demonstrate the use of synchrotron radiation Fourier Transform Infrared (SR-FTIR) microspectroscopy to analyse changes in the macromolecular composition of diatoms collected along the coast and plateau of Kerguelen Island, Southern Ocean. SR-FTIR microspectroscopy enabled the analysis of individual diatom cells from mixed communities of field-collected samples, thereby providing insight into in situ taxon-specific responses in relation to changes in Fe availability. Phenotypic responses were taxon-specific in terms of intraspecific variability and changes in proteins, amino acids, phosphorylated molecules, silicate/silicic acid and carbohydrates. In contrast to some previous studies, silicate/silicic acid levels increased under Fe enrichment, in conjunction with increases in carbohydrate stores. The highly abundant taxon <i>Fragilariopsis kerguelensis</i> displayed a higher level of phenotypic plasticity than <i>Pseudo-nitzschia</i> spp., while analysis of the data pooled across all measured taxa showed different patterns in macromolecular composition compared to those for individual taxon. This study demonstrates that taxon-specific responses to Fe enrichment may not always be accurately reflected by bulk community measurements, highlighting the need for further research into taxon-specific phenotypic responses of phytoplankton to environmental change.

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