EFFECTS OF LUMBRICIDS AND ENCHYTRAEIDS ON NEMATODES IN LIMED AND UNLIMED CONIFEROUS MOR HUMUS

In a factorial laboratory experiment, specimens of Dendrobaena octaedr a (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) were added to microcosms with unlimed (pH 4.5) and limed (pH 5.5) coniferous mor humus containing bacteria, fungi, protozoans, and nematodes. Effects o n the nematodes were assessed after an incubation period of 207 days a t 15-degrees-C and a soil moisture content of 60% water-holding capaci ty. When D. octaedra was absent, nematodes were significantly more abu ndant in the limed humus than in the unlimed humus. The presence of D. octaedra markedly reduced the number of nematodes in the limed humus but not in the unlimed one, where D. octaedra lost weight and probably did not feed. Most nematodes (92-97%) were bacterial-feeders. The pre sence of D. octaedra did not decrease the number or biomass of bacteri a, indicating that the reduction in nematode numbers was not the resul t of competition for bacteria between D. octaedra and the nematodes. T he presence of C. sphagnetorum had no effect on the nematodes in eithe r of the treatments. We suggest that the reason why D. octaedra, but n ot C. sphagnetorum, reduced nematode numbers is that the former was mo re likely to inadvertently ingest the nematodes because of its much gr eater size. The results provide a possible explanation for the observa tion that liming sometimes enhances nematode populations, when lumbric ids do not respond to the treatment, and sometimes causes decreases, w hen lumbricids increase in number.