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

Abstract

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.

Microbial food web dynamics during spring phytoplankton blooms in the naturally iron-fertilized Kerguelen area (Southern Ocean)

“…The macronutrient concentrations in the mixed layer were 20-30 µM for nitrate plus nitrite, 1-2 µM for phosphate, 8-24 µM for silicic acid ( Table 2, Blain et al, 2014;Closset et al, 2014) and dissolved iron ranged between 0.08 and 0.35 nM (Quéroué et al, 2014). According to KEOPS2's microscopical observations and pigment analysis, Bacillariophyceae dominated the phytoplankton community in the blooms (Sackett et al, 2014. In particular, Fragilariopsis kerguelensis, Pseudonitzschia spp., Eucampia antarctica, and Chaetoceros spp.…”

The fate of diatom valves in the Subantarctic and Polar Frontal Zones of the Southern Ocean: Sediment trap versus surface sediment assemblages

“…All the components of the "high export group" are thought to undergo rapid cell division during favourable growth conditions giving rise to the formation of large and rapidly sinking aggregates that are responsible for the deepest flux (e.g. Assmy et al, 2007;Smetacek et al, 2012;Grigorov et al, 2014;Sackett et al, 2014). We speculate that rapid export during the summer of 1999-2000 was a result of massive growth in these boom-and-bust strategists.…”

Single-Cell Biomolecular Analysis of Coral Algal Symbionts Reveals Opposing Metabolic Responses to Heat Stress and Expulsion

“…Formalin-fixed cells were loaded into a micro compression cell (modified compression cell, Spectratech Inc., Oak Ridge, USA; Tobin et al, 2010) with 1 mm thick CaF 2 window. Measurements were made on hydrated cells, a method shown to limit light scattering effects (Bambery et al, 2012;Sackett et al, 2014). Spectra were acquired over the measurement range 4,000-800 cm −1 with a Vertex 80v Fourier Transform Infra-Red (FTIR) spectrometer (Bruker Optics, Ettlingen, Germany) in conjunction with an IR microscope (Hyperion 3000, Bruker) fitted with a liquid nitrogen cooled mercury cadmium telluride detector.…”