Tolerance of resting cells of freshwater and terrestrial benthic diatoms to experimental desiccation and freezing is habitat-dependent

For a wide range of organisms, dormancy is a strategy to overcome adverse conditions in time and space, and one may expect that the stress tolerance of dormant stages is tuned to the habitat in which they occur. We assessed the tolerance of vegetative and resting cells of 17 benthic diatom morphospecies from habitats with contrasting permanency, ranging from moist soils to permanent lakes. Vegetative cells of all morphospecies were highly sensitive to desiccation and, except for strains of some terrestrial taxa, freezing. In contrast, resting cells of several morphospecies tolerated desiccation, especially when preceded by a heat treatment, and resting cells of more strains and morphospecies survived freezing, albeit often with low survival percentages and a large interstrain variation. Strikingly, all strains surviving desiccation and/or freezing belonged to terrestrial morphospecies, i.e. diatoms occurring mainly in wet and moist or temporary dry habitats outside water bodies. These results emphasize the importance of resting cells of terrestrial diatoms for the survival of stress tolerance, especially desiccation, and indicate specific adaptations of terrestrial diatoms to their highly variable habitats.