Articles | Volume 11, issue 20
Biogeosciences, 11, 5795–5808, 2014

Special issue: KEOPS2: Kerguelen Ocean and Plateau Study 2

Biogeosciences, 11, 5795–5808, 2014

Research article 20 Oct 2014

Research article | 20 Oct 2014

Taxon-specific responses of Southern Ocean diatoms to Fe enrichment revealed by synchrotron radiation FTIR microspectroscopy

O. Sackett1,2,3, L. Armand4, J. Beardall2, R. Hill5, M. Doblin1, C. Connelly6, J. Howes1, B. Stuart7, P. Ralph1, and P. Heraud2,3 O. Sackett et al.
  • 1Plant Functional Biology and Climate Change Cluster (C3), University of Technology, Sydney, New South Wales, Australia
  • 2School of Biological Sciences, Monash University, Victoria, Australia
  • 3Centre for Biospectroscopy, School of Chemistry, Monash University, Victoria, Australia
  • 4Department of Biological Sciences and Climate Futures, Macquarie University, New South Wales, Australia
  • 5Centre for Marine Bio-Innovation, University of New South Wales, New South Wales, Australia
  • 6School of Life and Environmental Sciences, Deakin University, Victoria, Australia
  • 7School of Chemistry, University of Technology, Sydney, New South Wales, Australia

Abstract. 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 Fragilariopsis kerguelensis displayed a higher level of phenotypic plasticity than Pseudo-nitzschia 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.

Final-revised paper