Osmotic stress in Arctic and Antarctic strains of the green alga Zygnema (Zygnematales, Streptophyta): Effects on photosynthesis and ultrastructure

► We investigate the osmotic potential of four polar green algal strains. ► We examine effects of osmotic stress on ultrastructure and photosynthesis. ► One investigated strain belongs to a different phylogenetic lineage. ► Arctic strains show higher osmotic values (more negative osmotic potentials). ► Physiological performance and ultrastructure are affected by osmotic stress.