Photosynthesis of two Arctic macroalgae under different ambient radiation levels and their sensitivity to enhanced UV radiation

The change in optimal quantum efficiency (F-v/F-m) of the Arctic species La minaria saccharina and Palmaria palmata was investigated in a long-term exp eriment in situ under different radiation levels during the summer of 1997 in the Kongsfjord (Ny-Alesund, Spitsbergen, Norway, 78 degrees 55.5'N, 11 d egrees 56.0'E). Whole plants were incubated in an open box system made of U V-transparent Perspex and exposed to solar radiation (lambda > 295 nm), sol ar radiation excluding UVB (lambda > 320 nm) and solar radiation excluding UVA + UVB (lambda > 400 nm). Increasing radiation levels were simulated by transplantation of the pre-adapted algae from their growth depth at 2 m to a water depth of 1 m. Sensitivity to artificially increased UV radiation wa s determined by exposure of algae from the three treatments to 6 h of stron g UV radiation. P. palmata was relatively insensitive to increasing UV radi ation and recovered very fast and almost completely in 2 h. Even plants pre -cultured in ambient radiation levels excluding UVA + UVB or UVB only showe d no photoinhibition after exposure to extra UV radiation in the laboratory . L. saccharina was, in comparison to P. palmata, more sensitive and showed photoinhibition under solar radiation and solar minus UVB radiation after transplantation from 2 to Im water depth. However, after 3 weeks at 1 m dep th, F-v/F-m of L. saccharina was equal in all treatments and restored to th e original values at the start of the experiment. Sensitivity to extra UV r adiation in the laboratory increased in time, although recovery was also fa st and occurred within 20 h.