AN ECOLOGICAL STUDY ON ECOSYSTEM FUNCTION OF JAPANESE MEGASCOLECID EARTHWORMS IN FOREST SOILS

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Megascolecid earthworms are dominant in Japanese soil, however there are very few studies on lice history and ecosystem function of megascolecid earthworms. We investigated life history of dominant earthworms at two forest sites in Kanagawa Pref. Epigeic species had annual life cycle ; they over wintered as eggs and grew quickly from June to July, then reproduced died in summer. Whereas endogeic species had longer life history and over wintered as juveniles and adults, and reproduction was observed during early summer to autumn. At Tomakomai Experimental Forest of Hokkaido University, epigeics were Megescolecidae, and endogeic species was Lumbricidae. Life history pattern was similar to that of Kanagawa. Carbon and nitrogen isotope ratio of earthworms, litter, soil were measured at forest soils in Hokkaido, Kanagawa and northern Okinawa. Both C and N stable isotopes were enriched from litter to deeper soil. Earthworm isotope rations were correlated to life history ; epigeics showed lighter and endogeics showed heavier isotope ration. Amynthas yambaruensis had ligher isotope ration, and this confirmed anecic life history of this species. Enzyme analysis of gut contents and gut wall showed that epigeic tends to have weaker enzyme activities, whereas endogeics have higher enzyme activites suggesting that endogeic earthworms utilize more recalcitrant organic matters in soil.