TISSUE CARBON-SOURCES FOR PONTOSCOLEX-CORETHRURUS (OLIGOCHAETA, GLOSSOSCOLECIDAE) IN A SUGARCANE ECOSYSTEM

The pantropical, geophagous earthworm species Pontoscolex corethrurus (Müller) is common in lowland soils supporting sugarcanc in notheastern Queensland. In comparison with situations where harvest residues are burned, its populations are substantially increased under cultural treatments in which harvest residues are retained as a surface mulch or are mechanically incorporated into the topsoil. The δ 13C values of stem and leaf materials, soil organic matter and the earthworm whole-body tissues and casts were determined. It is unlikely that P. corethrurus assimilates much of its tissue C from the more complex fractions of soil organic matter or directly from decomposing residues, at least until a late stage of breakdown. No differences in δ513C values were apparent in samples of this species from the different cultural treatments. From field observations of an intimate association between P. corethrurus and the sugarcane roots, we suggest that this species may derive much of its tissue C from rhizospherc sources. © 1990.