UV-B radiation induced changes in litter quality affects earthworm growth and cast characteristics as determined by metabolic fingerprinting

We investigated whether exposure to UV-B results in biochemical changes in leaf litter, affecting growth rates of earthworms feeding on this litter and cast chemistry. Seedlings of Betula pubescens L. were grown under zero and ambient UV-B (at 52 °N) regimes under optimal conditions. Following three months exposure, plants were allowed to senesce and leaf litter was collected. Lumbricus terrestris and Lumbricus rubellus were offered three substrates – processed oat grain, zero UV-B leaf litter and ambient UV-B leaf litter. Fourier transform infrared spectroscopy (FT-IR) analyses indicated that these substrates differed markedly in their composition, showing separation according to UV-B treatment and oat grain. There were no significant effects of UV-B treatment on the mass of earthworms feeding on litter, although trends suggested that L. rubellus benefited from the UV-B treated litter whilst L. terrestris showed the converse response. FT-IR analyses of L. terrestris casts showed more consistent differences in their biochemistry than was the case for litter. UV-B induced changes in living leaf material introduced to soil, even after earthworm processing, may have implications for cast microbial communities and nutrient cycling.