USE OF C-13 VARIATIONS AT NATURAL ABUNDANCE FOR STUDYING THE BIODEGRADATION OF ROOT MUCILAGE, ROOTS AND GLUCOSE IN SOIL

Variations in the natural abundance of C-13 in the CO2 evolved during the biodegradation of three substrates derived from maize plants provide a way of studying the decomposition of plant material in soil. The delta C-13 isotopic composition of the CO2 evolved (called deltaC) was followed during the decomposition of root mucilage, roots and glucose (initial composition deltaS), all from maize plants, in sand inoculated with a soil extract. Results indicate that a negative isotopic enrichment (epsilon = deltaC - deltaS < 0) occurred at the beginning and end of the decomposition process, whatever the substrate. For the intermediate stages of mineralization, the isotopic enrichment was small (deltaC slightly less than deltaS), or negligible. It is possible to take this enrichment effect into account in biodegradation studies, by introducing a correction factor in the calculation of the true mineralization rate. During the decomposition of the three substrates in soil, the correction factor varied between 1.04 and 1.08 for root mucilage, 1. 13 and 1.17 for roots and 1.13 and 1.27 for glucose.