Effects of physical factors on the survival and growth of antarctic terrestrial algae

The survival and growth of four genera of cyanobacteria and microalgae isolated from Antarctic fellfield soils were investigated. Survival of freezing and desiccation were studied by vital staining, and the effects of photon flux density (PFD) and temperature on growth rates were determined by direct counts of cultures maintained on a thermogradient bar. Monitoring of seasonal changes in environmental factors in a fellfield ecosystem demonstrated that the experiments were carried out under ecologically relevant conditions.The coccoid chlorophyte Planktosphaerella exhibited the highest growth rates under most conditions. Growth rates of the other species were similar to each other, although the diatom Pinnularia maintained near-maximum growth rates over a wider range of conditions than the filamentous cyanobacterium Phormidium or the filamentous chlorophyte Zygnema. Maximum growth of all species occurred at 15–20°C and no growth was observed at 0°C, indicating that there is little adaptation to growth at low temperature. Optimal PFD was generally 100–400 μmol m s and photoinhibition of growth occurred at a PFD significantly lower than that incident on the soil surface, even on cloudy days. Such results are consistent with the observation that the soil flora largely occurs beneath the surface of the soil where PFD is reduced.All species survived repeated 24 h freeze-thaw cycles, following an initial decline on the first cycle. Survival of desiccation differed markedly between species, from a few hours in Planktosphaerella to many weeks in Phormidium and Pinnularia, and is probably a major factor in the ability of these genera to colonize the fellfield soils