PROGRESSES IN THE STUDY OF CARBON ISOTOPES TRACING OF THE SOIL CARBON DYNAMICS

Soils are the largest carbon reservoir in terrestrial ecosystems. Soil organic matter contains generally three identifiable carbon pools: "active" pool; "slow" pool and "passive" pool. The dynamics of the soil carbon cycle focus on mostly carbon turnover times and input rates and size of soil carbon pools on various time scales. Many researchers indicated that natural abundance of carbon isotopes, in particular radiocarbon,is useful tracers in the study of the soil carbon cycle. δ~ (13)C values of soil organic matter provide a unique tool for quantifying historical shifts between C3 and C4 ecosystems over decadal to millennial time scales.~ (14)C signature, the combination of~ (14)C dating and~ (13)C signature can be used to determine the size and turnover rates of the labile and stable soil organic matter pools. Despite the advances in the study of the soil carbon cycle by means of carbon isotopes signature in recent decades, the isotopic approaches to the study of the soil carbon cycle have limitations. Tremendous uncertainties exist in the estimation of sizes and turnover times of soil carbon pools as well as the amount of~ (14)C content of SOM derived CO(2) because of a lack of reliable global database and a lack of standard methods available to quantify labile and stable soil organic matter pools. It is very difficult to estimate any change in the size of the soil C pool that could potentially alter the atmospheric CO(2) concentration and the global climate.