13C/12C isotopes of leaf wax lipids in soil profiles to establish vegetation changes at Strathdarr, Queensland

This study has been undertaken to determine whether a significant difference in 13C/12C of grass-derived char (C3 and C4) compared with wood-derived (C3) char is apparent. Our data showed a depletion of up to 8 per mil in C4-derived chars from natural burns, yet there was no significant isotopic change in chars from wood or C3 grasses. We suggest that this -13C depletion in C4-derived chars is due to protected organic matter in silicate structures (phytoliths), which were found to be depleted by up to 9 per mil. Analysis of this protected carbon by Py-GC-MS indicated the presence of low relative amounts of n-alkanes, whereas FTIR and 13C-NMR analyses suggested that a significant portion of the material was composed of simple carbohydrates. These isotopic and spectroscopic data have important implications for the calculation of the proportions of C3- versus C4-derived charred organic matter in modern, as well as geologic, studies.

Personnel

E. Krull, K. Grice, A. Bowater

Funding

CSIRO Land and Water

Collaborators

CSIRO Land and Water