The spatial distribution of microalgae on Antarctic fellfield soils

The horizontal and vertical distributions of cyanobacteria and algae on soil polygons on Signy Island were investigated. Soil chlorophyll concentrations increased from the centre to the edge of the polygons. Similar distributions of the non-motile genera, such as Pseudanabaena and Nostoc, were observed, whereas the motile taxa, Phormidium and Pinnularia, were evenly distributed across the polygon. Phormidium autumnale was the most widespread taxon, and other Oscillatoriaceae were also important, although large differences in community composition between polygons were observed. Most of the algal biomass was concentrated near the surface of the soil, although chlorophyll degradation products were found to depths of up to 8 cm. Examination of the soil profile by fluorescence microscopy indicated that a large proportion of the microflora occurred in the zone 0–1 mm below the surface, and scanning electron microscopy confirmed that few algae occurred on the soil surface. It is suggested that this may be a desiccation-avoidance strategy. Vertical migration of the motile microalgae to the soil surface was not observed in the field, but could be induced in the laboratory in the presence of excess water, although no diel cycle to this movement was observed.