Isotope discrimination during decomposition of organic matter: A theoretical analysis

Stable isotope composition is a powerful characteristic of the development of soil organic matter, but there is a need to understand the causes of and to predict the changes in isotopic composition during organic matter decomposition. We used the continuous quality theory to derive a set of equations to analyze how properties of the litter interact with properties of the decomposers to produce different patterns of isotopic composition. The distribution of isotopes between different chemical fractions in the litter is in itself such that it should lead to increasing depletion of C-13 during the course of decomposition. Isotope effects on decomposer growth rate, efficiency, and dispersion In quality increase, on the other hand, C-13 concentration. The magnitudes of these effects have to be, in relative terms, considerably greater than that of initial litter chemical composition. The equations derived were also successfully tested on experimentally observed patterns of changes in C isotopic composition in an agricultural soil and some forest soils.