Solar UV-B radiation, associated with ozone depletion, inhibits the Antarctic terrestrial microalga, Stichococcus bacillaris

This study shows that increased UV-B arising from stratospheric ozone depletion over Antarctica reduced cell viability and the maximum quantum yield of photochemistry (Fv/Fm) in a unicellular terrestrial microalga, Stichococcus bacillaris. In the UV waveband, rates of Fv/Fm decline increased with decreasing wavelength. Photosynthetically active radiation (PAR) also reduced Fv/Fm, though less than UV radiation. Further experiments under different ozone column thicknesses showed a significantly greater decline in cell viability and Fv/Fm under ozone depletion compared with non-depleted conditions. The inhibitory effects of ambient solar radiation suggest that S. bacillaris is unlikely to inhabit soil surfaces, but colonises shaded areas beneath soil surface particles. During periods of ozone depletion, increases in the ratio of UV-B:PAR may reduce the thickness of the sub-surface zone where light conditions are suitable for colonisation by this alga.