Tolerance of pennate diatoms (Bacillariophyceae) to experimental freezing: comparison of polar and temperate strains

ABSTRACTAlthough polar regions are characterised by extreme environment conditions with overall low temperatures and often pronounced diurnal to seasonal temperature fluctuations, diatoms (Bacillariophyceae) thrive in a wide range of nonmarine polar habitats, suggesting that they are well adapted to these harsh conditions. In this study, tolerance to freezing of vegetative and resting cells of 17 polar and nine temperate diatom strains, belonging to different morphospecies and originating from both freshwater and terrestrial habitats, was experimentally tested. Most strains were newly isolated from sites in Maritime Antarctica (James Ross Island and Vega Island), the High Arctic (Spitsbergen) and Europe. Cultures were exposed to five freezing treatments differing in temperature (−4, −20, −40 and −180 °C), freezing rate (gradual, abrupt), time (1 h, 12 h) and thawing rate (slow, fast). Results indicated that diatoms were sensitive to experimental freezing. Freezing temperatures had a significant effect on ...