ISOTOPE DISCRIMINATION DURING DECOMPOSITION OF ORGANIC-MATTER - A THEORETICAL-ANALYSIS

Stable isotope composition is a powerful characteristic of the develop ment of soil organic matter, but there is a need to understand the cau ses of and to predict the changes in isotopic composition during organ ic matter decomposition. We used the continuous quality theory to deri ve a set of equations to analyze how properties of the litter interact with properties of the decomposers to produce different patterns of i sotopic composition. The distribution of isotopes between different ch emical fractions in the litter is in itself such that it should lead t o increasing depletion of C-13 during the course of decomposition. Iso tope effects on decomposer growth rate, efficiency, and dispersion In quality increase, on the other hand, C-13 concentration. The magnitude s of these effects have to be, in relative terms, considerably greater than that of initial litter chemical composition. The equations deriv ed were also successfully tested on experimentally observed patterns o f changes in C isotopic composition in an agricultural soil and some f orest soils.