THE STABLE ISOTOPIC COMPOSITION AND MEASUREMENT OF CARBON IN SOIL CO2

Abstract

The theoretical minimum difference between the δ13C of soil CO2 (a concentration) and soil-respired CO2 (a flux) was previously thought to be 4.4%%. It is shown here that the difference is a function of the δ13C of soil-respired CO2, with possible minimum values less than 4.4%%. A simple equation is given which allows the δ13C of soil CO2 or soil-respired CO2 to be calculated from four measurable variables. Sampling methodology is investigated demonstrating the need for correcting measured soil-respired CO2 samples for CO2 contamination in base reagents, for contributions from atmospheric CO2, and for isotopic fractionation at the base-solution/air interface.