EFFECTS OF DECOMPOSITION OF LEAVES ON BACTERIAL BIOMASS AND ON PALATABILITY TO LUMBRICUS-TERRESTRIS L

The decomposition of leaves of Taraxacum officinale, Hypericum perfora tum, Dipsacus silvester and Miscanthus sinensis was monitored under la boratory conditions (20 degrees C, 90 to 100% relative humidity) for 2 to 4 weeks. At weekly intervals, weight loss, C-to-N-ratio, Secondary plant metabolites, bacterial biomass and palatability to the earthwor m Lumbricus terrestris were determined. The first order constants for dry weight loss were 0.092, 0.012, 0.005 and 0.004 d(-1) for T. offici nale, H. perforatum, D. silvester and M. sinensis, respectively. Secon dary metabolites in green leaves of all plants mainly comprised polyph enolic compounds (bitter drugs, coumarins, flavonoids). During initial decomposition, the overall pattern of secondary plant metabolites was characterized by a qualitative and quantitative reduction. After one week of decomposition, the patterns of secondary plant metabolites bec ame similar in all species and remained visually unchanged during furt her decomposition. A potential inhibition of bacterial growth and pala tability to L. terrestris could be demonstrated ill bioassays with ext racts of secondary plant metabolites from H. perforatum and D. silvest er. On plants, however, an inhibition of bacterial growth and a reduct ion of palatability to L. terrestris was only obtained during the init ial decomposition of senescent leaves of H. perforatum which is known to possess toxic secondary plant metabolites. The bacterial growth and the palatability to L. terrestris on leaves of T. officinale, D. silv ester and M. sinensis were mainly influenced by the C-to-N-ratio of th e leaves. (C) 1998 Elsevier Science Ltd. All rights reserved.