The effects of millipedes (Harpaphe haydeniana) on microbial decomposition of leaf litter

Most estimates of litter decomposition rates do not account well for the effects of soil macrofauna, and so are suspect in ecosystems in which litter-transforming soil fauna are abundant. In coastal rainforests, millipedes consume substantial amounts of leaf litter, most of which is egested as faecal pellets. Little is known about the fate of this material, which hinders estimation of realistic rates of litter decomposition in these ecosystems. In this study, I assess the influence of feeding by the millipede (Harpaphe haydeniana) on decomposition of leaf litter by comparing rates of CO₂ release during laboratory incubation from leaf litter which has been ingested by millipedes and transformed into faecal pellets with that from litter which has not been ingested by millipedes. Changes in litter microbial communities as a consequence of millipede ingestion are assessed by comparing the PLFA profiles of faeces and uningested litter during incubation. Rates of CO₂ release from faeces and litter were similar. CO₂ release was higher in maple litter than Douglas-fir litter, and this difference persisted in the faeces from litter that millipedes fed on. Differences in bacterial abundance between litter types were also retained during millipede gut passage. Grinding of litter increased CO₂ release, as did grinding of faeces, indicating that structure of litter and millipedes’ faecal pellets may restrict microbial access and thus decrease the decomposition rates. Microbial activity and abundance did not differ between leaf litter and faeces incubated alone vs together.Forestry, Faculty ofGraduat