MICROBIAL CONDITIONING OF LEAF-LITTER AND FEEDING BY THE WOOD-LOUSE PORCELLIO SCABER

Microbial standing crops in decomposing oak and beech litters were mea sured in the laboratory by direct observation methods based on fluores cence staining. Bacterial cells and fungal hyphae both increased durin g incubation, reaching a maximum between 2 and 4 weeks, and thereafter declined. The peaks of microbial standing crops, which were less than 1% above levels in leaves at the beginning of decomposition, co-incid ed with the highest rates of feeding and defaecation by the wood-louse Porcellio scaber. This indicates that feeding rates of P. scaber migh t not only be related to increases of microbial standing crops in the leaves (usually associated with the detoxification of allelochemicals or the immobilisation of nutrients from the soil solution), but also t o decreases of microbial standing crops (associated with a depletion o f digestible C-and N-sources of plant and microbial origin).