Stable C and N isotope values of selected components of a tropical australian sugarcane ecosystem

Abstract

The δ13C and δ15N values of sugarcane plant tissues, decomposing harvest residues, soil and the casts and body tissues of the earthwormPontoscolex corethrurus were determined. Little variation in δ13C values was found between plant parts. The δ13C values of the decomposing harvest residues declined and became more variable after 148 days of exposure in the field. In the decomposing residues, δ13C values of the neutral detergent fibre fraction were similar to those of the whole tissues while those of the proximate lignin were more negative. The δ15N values of the residues also declined over time after a short initial delay.P. corethrurus populations are more intimately associated with the roots of sugarcane than with the bulk soil. Tissue δ13C values suggest that the earthworm diet is similar to or more enriched in13C than sugarcane tissues and is substantially more enriched than the soil C. Earthworm tissues have similar levels of15N enrichment to both the soil and plant tissues. These data are consistent with the hypothesis that this earthworm derives much of its assimilated C relatively directly from organic matter associated with the roots and decomposing harvest residues.