Compatible solutes and fatty acid composition of five marine intertidal microphytobenthic Wadden Sea diatoms exposed to different temperature regimes

Abstract

Microphytobenthic organisms inhabiting marine intertidal areas are subjected to strongly changing temperature and surface light regimes due to evaporation at low tide. In addition, seasonal fluctuations in temperatures significantly influence the taxonomic composition of benthic diatom communities in intertidal flats. In order to determine the physiological responses of marine benthic diatoms to temperature changes, five common species (Achnanthes brevipes C.A. Agardh, Amphora arenaria Donkin,Cocconeis peltoides Hustedt, Navicula digitoradiata (Gregory) Ralfs and N. gregaria Donkin), isolated from the Solthörn tidal flats, were chosen to study the effect of different temperatures (4, 18 and 35°C) on the composition of intercellular free amino and fatty acids as well as the accumulation of polyols, saccharides and quaternary ammonium compounds (QUARCs) during short- (24 h) and long-term (30 d) exposures. Although the growth response of the five diatom taxa was hardly affected by temperatures in short-term temperature treatments, the growth rates were significantly lower after long-term treatments maintained at 4 and 35°C. Significant differences were found in physiological responses to temperature treatments of the species tested. In experimental temperature treatments, species accumulated proline, glycerol and glucose, whereas the species in high-temperature treatments also accumulated short-chain fatty acids. By contrast, the responses to low-temperature treatments comprised accumulation of the QUARCs homarine and glycine-betaine as well as β-dimethylsulfoniopropionate (DMSP) and polyunsaturated fatty acids (PUFAs). In conclusion, these results showed common resistance mechanisms to temperature stresses in marine benthic diatoms, with species-specific differences in compound composition (e.g., proline). The significant differences in osmolyte compositions of the five diatom taxa during high- and low-temperature exposure suggest a species-specific physiological acclimation that may explain their growth-insensitivity towards short-term temperature variations.