The direct effects of UV-B radiation on Betula pubescens litter decomposing at four European field sites

A co-ordinated series of field experiments were conducted to consider the e ffects of elevated UV-B radiation applied directly to decomposing plant lit ter. Betula pubescens was decomposed under ambient and elevated UV-B (simul ating a 15% ozone depletion) using outdoor irradiation facilities at Advent dalen, Norway (78 degrees N), Abisko, Sweden (68 degrees N), Amsterdam, The Netherlands (52 degrees N,) and Patras, Greece (38 degrees N). There was n o significant effect of treatment on mass loss for samples collected after 2, 12 and 14 months decomposition at Amsterdam, or after 4 months decomposi tion at Adventdalen. Significant reductions in the mass loss of litter deco mposing under elevated UV-B compared to ambient were found at the other 2 s ites. The only effect of treatment on litter chemistry during decomposition was a significant reduction in the N concentration of material at Abisko a nd a significant increase in C:N at Patras for litter decomposing under ele vated UV-B. Significant differences were found in the structure of the fung al community decomposing litter in Sweden, the only site to be tested. Thes e data, and the few published studies of the response of decomposition to U V-B incident on litter suggest that, in the ecosystems and climates that ha ve been studied, such direct effects are typically confined to the initial stages of decomposition, and are rather small in magnitude.