The effects of freezing and desiccation on photosynthesis and survival of terrestrial Antarctic algae and cyanobacteria

The effects of low temperatures, freezing and desiccation on a cyanobacterium (Phormidium) and an alga (Prasiola) from terrestrial Antarctic habitats were investigated. Net photosynthesis per unit dry weight, measured by gas exchange, and the vital stain Auramine O were used to monitor recovery from stress. Photosynthetic rates by Prasiola were an order of magnitude higher than those by Phormidium, although both continued photosynthesis at sub-zero temperatures. Prasiola survived freezing more readily, but in both cases survival was dependant upon the prevailing light conditions and the presence/absence of free water. Phormidium readily survived desiccation, whereas high mortality occurred in Prasiola, particularly at high light intensities. The results obtained are discussed in relation to the habitat and ecology of the organisms.