UV-B tolerance of bryophyte species with different degrees of desiccation tolerance

We report on the efficiency of the primary photochemistry of photosystem II and potential thylakoid activity (represented by the variable fluorescence decrease ratio) of seven UV-B-treated bryophyte species during exposure an d the subsequent recovery period. In Tortula ruralis, a strongly desiccatio n-tolerant grassland moss, there is no indication of any effects of W-B irr adiation. Desiccation-tolerant forest mosses (Polytrichum formosum, Mnium h ornum) are only temporarily affected by W-B radiation or can even be positi vely affected by it (Dicranum scoparium). The protective mechanism of desic cation-sensitive mesic species (Plagiothecium undulatum, Leucobryum glaucum , Pellia epiphylla) is rapidly exhausted and they cannot tolerate increased UV-B radiation. These results support our view presented here that desicca tion tolerance and UV-B tolerance involve similar defence mechanisms. (C) 1 999 Elsevier Science S.A. All rights reserved.