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

The ¹³C and ¹⁵N values of sugarcane plant tissues, decomposing harvest residues, soil and the casts and body tissues of the earthwormPontoscolex corethrurus were determined. Little variation in ¹³C values was found between plant parts. The ¹³C values of the decomposing harvest residues declined and became more variable after 148 days of exposure in the field. In the decomposing residues, ¹³C 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 ¹⁵N 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 ¹³C 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.