부산대학교 도서관

Assimilation of soil organic matter and fresh plant debris by Millsonia anomala, a tropical geophagous earthworm, was investigated by measuring changes in the [sup.13.C/sup.12.C] ratio of their tissues when fed on organic matter naturally labelled by [13.sup.C]. Individuals collected from a soil colonized by [C.sup.4] plants ([C.sup.4] soil) that were fed on [C.sup.3] soil had >50% of tissue C derived from the [C.sup.3] soil after 33 d. Assimilation of organic matter associated with different particle size fractions was investigated with individuals fed for 25 d on [C.sup.4] soil with [C.sup.4] particle size fractions substituted in turn for the equivalent [C.sup.3] soil particle fraction. A significant labelling of earthworms was observed with both the 250-200 [mu]m and the 0-20 [mu]m particle size fractions. Addition of fresh [C.sub.3] plants debris to the [C.sup.4] soil also resulted in a significant change in earthworm C isotope ratio. Assimilation of fresh plant material was greater than that of soil organic matter. This shows that young M. anomala are able to assimilate young organic matter (fresh plant debris, course oil organic matter) as well as fine soil organic matter, both of which classically have been regarded as strongly resistant to decomposition in models of soil organic matter dynamics. Key words: assimilation; C isotope ratio; fresh plant debris; geophagous tropical earthworm; particle size organic fractions; soil organic matter.