THE IMPACT OF ENHANCED ULTRAVIOLET-B RADIATION ON LITTER QUALITY AND DECOMPOSITION PROCESSES IN VACCINIUM LEAVES FROM THE SUB-ARCTIC

The aim of this study was to investigate how UV-B radiation will affec t 1) the quality of plant litter grown under different UV-B levels in the Subarctic and 2) decomposition under different UV-B levels. The de ciduous dwarf shrubs Vaccinium uliginosum and V. myrtillus grew under ambient and enhanced UV-B (corresponding to 15% ozone depletion) in a natural heath ecosystem in the Subarctic. After two growing seasons se nesced leaves were collected and decomposed in a 2 x 2 factorial exper iment under both laboratory conditions for 62 d (V. uliginosum: no UV- B and 10 kJ m-2 d-1 UV-B(BE)) and under field conditions for twelve mo nths (V. myrtillus: ambient and enhanced UV-B corresponding 15% ozone depletion). Additionally, colonization and growth of decomposing fungi were studied on leaves decomposed without and with UV-B in the labora tory. The enhanced UV-B during growth changed the litter quality (decr ease in alpha-cellulose, increase in tannins). Subsequently the microb ial respiration was decreased. This and the decreased cellulose/lignin ratio may have led to the lower relative mass loss due to treatments as detected both after 62 d decomposition in the laboratory and after twelve months decomposition in the field. The UV-B during decompositio n decreased the proportion of lignin in the plant residues, which is p ossibly due to photodegradation by UV-B. Total microbial respiration d ecreased, indicating the decomposers' sensitivity to UV-B. In general, the litter decomposing under UV-B was less colonized by fungal decomp osers. Mucor hiemalis and Truncatella truncata were significantly more abundant in the control, indicating sensitivity to UV-B radiation, wh ile Penicillium brevicompactum was equally abundant in the UV-B and co ntrol. There is strong indication of a change in decomposer fungal com munity structure due to UV-B. Just one of the three fungal species com mon on the control litter was dominant on leaves decomposed under UV-B .