SIGNIFICANCE OF EARTHWORMS IN STIMULATING SOIL MICROBIAL ACTIVITY

The stimulatory effect of earthworms (Lumbricus terrestris is L.) on s oil microbial activity was studied under microcosm-controlled conditio ns. The hypothesis was tested that microbial stimulation observed in t he presence of a soil invertebrate would be due to the utilization of additional nutritive substances (secretion and excretion products) tha t it provides. Changes in microbial activity were monitored by measuri ng simultaneously CO2 release and protozoan population density. The in crease in CO2 released in the presence of earthworms was found to resu lt from both earthworm respiration and enhanced microbial respiration. The stimulation of microbial activity was confirmed by a significant increase in protozoan population density, which was 3-19 times greater in the presence of earthworms. The respiratory rate of L. terrestris was estimated to be 53 mu l O-2 g(-1) h(-1). Earthworm respiration sig nificantly correlated with individual earthworm weight, but there was no correlation between the increase in microbial respiration and earth worm weight. This finding does not support the hypothesis given above that enhanced microbial respiration is due to utilization of earthworm excreta, A new hypothesis that relationships between microbial activi ty and earthworms are not based on trophic links alone but also on cat alytic mechanisms is proposed and discussed.