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 sphagnetorum (Vejdovsky) on microbial respiration and hyphal length in soil. In a feeding experiment we established that C. sphagnetorum feeds on the fungus Mortierella isabellina (Oudem) and that the worms disperse fungal propagules. Grazing of C. sphagnetorum with densities ranging from 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 natural microflora and fauna; and (2) a 2-species set up with C. sphagnetorum and M. isabellina inoculated into a sterillized soil. In the natural soil high densities of enchytraeids clecreased microbial respiration but no effects were found of enchytraeid grazing on the lengths of fungal hyphae. After 1 wk, in the 2-species soil, respiration of M. isabellina was higher in all experiments with enchytraeids present compared to controls with only the fungus. The hyphal lengths of M. isabellina in the inoculated soil increased about 2- to 3-fold at the lowest intensities of grazing but decreased to that of an ungrazed soil at the highest level of grazing.