Negligible influence of elevated UV-B radiation on leaf litter quality of Quercus robur

We tested whether elevated UV-B radiation applied to Quercus robur, a princ ipal climax species of northern Europe, would influence concentrations of p olyphenolics (Folin-Denis tannins and lignin), phenylpropanoid moieties of lignin, carbohydrates (monosaccharides and holocellulose), or nutrient elem ents (K, Ca, Mg, P and N) in recently-abscised leaf litter. Saplings of Q. robur were exposed for 2 years at an outdoor facility in the UK to a 30% el evation above the ambient amount of erythemally-weighted UV-B (280-315 nm) radiation under arrays of fluorescent lamps with cellulose diacetate filter s, which transmitted both UV-B and UV-A (315-400 nm) radiation. Saplings we re also exposed to elevated UV-A alone under arrays of lamps with polyester filters and to ambient radiation under non-energised arrays of lamps. We f ound little evidence that elevated UV-B radiation influenced leaf litter qu ality. Data pooled for both years indicated an 8% increase in vanillic acid concentration in litter from polyester-filtered lamp arrays, relative to n on-energised arrays, and 8% and 6% increases, respectively, in concentratio ns of acetovanillone in litter from polyester- and cellulose diacetate-filt ered lamp arrays, relative to non-energised lamp arrays. Arabinose concentr ation in litter from cellulose diacetate-filtered lamp arrays was 3%, highe r than in litter from polyester-filtered arrays, and glucose concentration in litter from cellulose-diacetate filtered lamp arrays was increased by 6% , relative to non-energised arrays. There were no main effects of elevated UV on the concentrations of holocellulose, polyphenolics or nutrient elemen ts. We conclude that exposure to elevated UV-B does not substantially influ ence the initial chemical composition of Q. robur leaf litter and that any increases in UV-B radiation arising from ozone depletion over northern mid- latitudes will be unlikely to affect nutrient cycling and decomposition in Quercus woodlands through effects on litter quality alone. (C) 2001 Elsevie r Science Ltd. All rights reserved.