ON THE ISOTOPIC COMPOSITION OF CARBON IN SOIL CARBON-DIOXIDE

In this study it is shown that the isotopic composition of carbon in soil CO2 differs from the isotopic composition of carbon in soil-respired CO2. Soil CO2 collected from a montane soil has an endmember delta-C-13 value of -23.3 parts per thousand whereas soil-respired CO2 in this system has a delta-C-13 value of -27.5 parts per thousand. This difference is very close to the theoretical difference of 4.4 parts per thousand which is predicted by the difference in the diffusion coefficients for (CO2)-C-12 and (CO2)-C-13. Because of the measured and the theoretical difference between the isotopic composition of carbon in soil CO2 and soil-respired CO2 it is suggested that, in the future, a distinction should be made between them.