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

[摘要] Photosynthesis by marine diatoms contributes substantially to globalbiogeochemical cycling and ecosystem productivity. It is widely accepted thatdiatoms are extremely sensitive to changes in Fe availability, with numerousin situ experiments demonstrating rapid growth and increased export ofelements (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 ofdiatoms, such as associated changes in nutritional value – furthermore, data ontaxon-specific responses are almost non-existent. Enhanced supply ofnutrient-rich waters along the coast of the subantarctic Kerguelen Islandprovide a valuable opportunity to examine the responses of phytoplankton tonatural Fe enrichment. Here we demonstrate the use of synchrotron radiationFourier Transform Infrared (SR-FTIR) microspectroscopy to analyse changes inthe macromolecular composition of diatoms collected along the coast andplateau of Kerguelen Island, Southern Ocean. SR-FTIR microspectroscopyenabled the analysis of individual diatom cells from mixed communities offield-collected samples, thereby providing insight into in situtaxon-specific responses in relation to changes in Fe availability.Phenotypic responses were taxon-specific in terms of intraspecificvariability and changes in proteins, amino acids, phosphorylated molecules,silicate/silicic acid and carbohydrates. In contrast to some previousstudies, silicate/silicic acid levels increased under Fe enrichment, inconjunction with increases in carbohydrate stores. The highly abundant taxonFragilariopsis kerguelensis displayed a higher level of phenotypicplasticity than Pseudo-nitzschia spp., while analysis of the datapooled across all measured taxa showed different patterns in macromolecularcomposition compared to those forindividual taxon. This study demonstratesthat taxon-specific responses to Fe enrichment may not always be accuratelyreflected by bulk community measurements, highlighting the need for furtherresearch into taxon-specific phenotypic responses of phytoplankton toenvironmental change.

[学科分类] 地球化学与岩石