DIRECT EFFECTS OF ELEVATED UV-B RADIATION ON THE DECOMPOSITION OF QUERCUS-ROBUR LEAF-LITTER

Decomposing Quercus robur L. leaf litter was exposed for 64 weeks at a n outdoor facility to supplemental levels of UV-B radiation (280-315 n m) under treatment arrays of cellulose diacetate-filtered fluorescent lamps which also produce UV-A radiation (315-400 nm). Litter was also exposed to UV-A radiation alone under control arrays of polyester-filt ered lamps and to ambient levels of solar radiation under arrays of un energised lamps. The treatment corresponded to a 30% elevation above t he ambient erythemally-weighted level of UV-B radiation. Litter was sa mpled after 11, 39 and 64 weeks and was examined for differences in ma ss loss, decomposition constants (k), chemical composition and the abu ndances of saprotrophic fungi. No effects of UV radiation on k values were recorded, bur after 11 weeks, percentage mass loss of litter expo sed to UV-B radiation under treatment arrays was 3% lower than under c ontrol arrays and 2% lower than under ambient arrays. After 39 weeks, litters exposed to UV-A radiation under control arrays had 10% lower t otal nitrogen contents and 13% higher C:N ratios than those litters ex posed beneath ambient arrays. At the last sampling, litters exposed to supplemental UV-B radiation had 5% higher carbon contents than those under ambient arrays. A 2.4-fold increase in the frequency of lamina p articles of litter that were uncolonised by fungi was recorded in litt er exposed to UV-B radiation under treatment arrays, compared to ambie nt arrays. The abundances of the saprotrophic fungi Cladosporium spp. and Acremonium pelsicinum (Nicot) W. Gams were decreased by 50% and 91 %, respectively, under UV-B treatment arrays compared to ambient array s, and the abundance of coelomycete conidiomata recorded on leaves was increased by 12% under treatment arrays, compared to ambient. Dactyle lla spp. were not recorded on litter exposed to UV-A radiation under c ontrol arrays and UV-A radiation applied under control and treatment a rrays apparently increased the abundance of Polyscytalum fecundissimum Riess. on litter. UV radiation had fewer effects on the abundances of decomposer fungi that develop in leaf tissues than it did on those th at develop on leaf litter surfaces. We conclude that increased fluxes of UV-B radiation as a result of stratospheric ozone depletion will ha ve subtle but wide ranging impacts on the decomposition of litters in oak woodlands.