Photophysiological investigations of the temperature stress responses of Zygnema spp (Zygnematophyceae) from subpolar and polar habitats (Iceland, Svalbard)

Zygnematophyceae are main primary producers in polar hydro-terrestrial habitats, characterized by extreme abiotic conditions. They are expected to be strongly impacted by climate change, leading to threats to subpolar and polar ecosystems. Two isolates of Zygnema from a subpolar (Iceland, Zygnema sp. I) and a polar Island (Svalbard, Zygnema sp. B) were compared by their photophysiological performance and phenolic content. A phylogenetic analysis was performed in a newly isolated Zygnema I where also morphology and ultrastructure were characterized. The rbcL sequence of the Icelandic Zygnema I was identical to that of Zygnema V, previously isolated from Svalbard, and phylogenetic analysis placed this strain into Zygnema clade 2. Average width of vegetative filaments (28 +/- 0.7 mu m) and ultrastructure was similar to closely related Zygnema strains. Zygnema I and Zygnema B were exposed to three different treatment temperatures (15, 20 and 25 degrees C) for two weeks, then photophysiological parameters and cellular phenol contents were acquired. The maximum electron transport rate increased significantly with elevated temperatures, but non-photochemical quenching did not change. Net photosynthetic oxygen production was higher in Zygnema B, but decreased in both strains from 10 to 15 degrees C measuring temperature. Zygnema I showed a significant decrease between 15/25 degrees C-treated cultures above 20 degrees C measuring temperature. The phenolic content did not change significantly with experimental treatments, the spectral absorption at 350 nm was significantly lower in Zygnema B when compared with Zygnema I. Taken together our results indicate that Zygnema B and Zygnema I cannot adapt to elevated temperatures.

Automated summary

This study compares the photophysiological performance and phenolic content of two isolates of Zygnema from subpolar and polar regions. The results show that Zygnema strains cannot adapt to elevated temperatures.