EFFECTS OF UV RADIATION ON A CHLOROPHYTE ALGA (SCENEDESMUS SP.) ISOLATED FROM THE FUMAROLE FIELDS OF MT. EREBUS,ANTARCTICA1

Acclimation to UV radiation (UVR) was examined in a unicellular chlorophyte isolated from fumarole fields adjacent to Mt. Erebus, Antarctica. Long‐term exposure to UVR (14 days) initially reduced the efficiency of photosynthetic energy conversion measured as the dark adapted quantum yield of PSII fluorescence (F_v/F_m) when compared with cultures not exposed to UVR. However, the UVR exposed cultures recovered to pre‐UVR exposure levels of photosynthetic efficiency by the end of the experimental period. Additionally, neither growth rates nor cell size were significantly affected by exposure to UVR. In contrast, the maximum rate of carbon fixation on a chl a basis was significantly reduced at the end of the experiment and was accompanied by a significant decrease in chl a concentrations. These results suggest a transient effect of UVR on primary photochemistry consistent with damage to PSII, possibly at the D1 protein, with more chronic effects on carbon fixation that did affect maximum photosynthetic capacity. Ultrastructural and molecular (18s rDNA) data show that this isolate from the fumoral fields of Mt. Erebus, Antarctica is a member of the genus Scenedesmus.