Elevated UV-B radiation incident on Quercus robur leaf canopies enhances decomposition of resulting leaf litter in soil

We examined whether the exposure of Quercus robur L. to elevated UV-B radia tion (280-315 nm) during growth would influence leaf decomposition rate thr ough effects on litter quality. Saplings were exposed for eight months at a n outdoor facility in the UK to a 30% elevation above the ambient level of erythemally weighted UV-B radiation under UV-B treatment arrays of fluoresc ent lamps filtered with cellulose diacetate, which transmitted both UV-B an d UV-A (315-400 nm) radiation. Saplings were exposed to elevated UV-A alone under control arrays of lamps filtered with polyester and to ambient radia tion under unenergised arrays of lamps. Abscised leaves from saplings were enclosed in 1 mm(2) mesh nylon bags, placed in a Quercus-Fraxinus woodland and were sampled at 0.11, 0.53,1.10 and 1.33 years for dry weight loss, che mical composition and saprotrophic fungal colonization. At abscission, litters from UV-A control arrays had approximate to 7.5% hig her lignin/nitrogen ratios than those from UV-B treatment and ambient array s (P < 0.06). Dry weight loss of leaves treated with elevated UV-B radiatio n during growth was 2.5% and 5% greater than that of leaves from UV-A contr ol arrays at 0.53 and 1.33 years, respectively. Litter samples from UV-B tr eatment arrays lost more nitrogen and phosphorus than samples from ambient arrays and more carbon than samples from UV-A control arrays. The annual fr actional weight loss of litter from UV-B treatment arrays was 8% and 6% gre ater than that of litter from UV-A control and ambient arrays, respectively . Regression analyses indicated that the increased decomposition rate of UV -B treated litters was associated with enhanced colonization of leaves by b asidiomycete fungi, the most active members of the soil fungal community, a nd that the frequency of these fungi was negatively associated with the ini tial lignin/nitrogen ratio of leaves.