EFFECTS OF ENCHYTRAEID GRAZING ON FUNGAL GROWTH AND RESPIRATION

In view of the grazing optimization theory, we examined the effects of different intensities of grazing by the enchytraeid Cognettia sphagne torum (Vejdovsky) on microbial respiration and hyphal length in soil. In a feeding experiment we established that C. sphagnetorum feeds on t he fungus Mortierella isabellina (Oudem) and that the worms disperse f ungal propagules. Grazing of C. sphagnetorum with densities ranging fr om 0 to 54,000 enchytraeids m(-2) was studied in 2 experiments: (1) a multi-species system with C. sphagnetorum kept in soil with its natura l microflora and fauna; and (2) a 2-species set up with C. sphagnetoru m and M, isabellina inoculated into a sterilized soil. In the natural soil high densities of enchytraeids decreased microbial respiration bu t no effects were found of enchytraeid grazing on the lengths of funga l hyphae. After 1 wk, in the 2-species soil, respiration of M. isabell ina was higher in all experiments with enchytraeids present compared t o controls with only the fungus. The hyphal lengths of M. isabellina i n the inoculated soil increased about 2- to 3-fold at the lowest inten sities of grazing but decreased to that of an ungrazed soil at the hig hest level of grazing.