Using natural ¹³C abundances to differentiate between three CO₂ sources during incubation of a grassland soil amended with slurry and sugar

This study describes a novel approach to separate three soil carbon (C) sources by one tracer method (here 13 C natural abundance). The approach uses the temporal dynamics of the CO 2 efflux from a C 3 grassland soil amended with added C 3 or C 4 slurry and/or C 3 or C 4 sugar to estimate contributions of three separate C sources (native soil, slurry, and sugar) to CO 2 efflux. Soil with slurry and/or sugar was incubated under controlled conditions, and concentration and δ 13 C values of evolved CO 2 were measured over a 2‐week period. The main assumption needed for separation of three C sources in CO 2 efflux, i.e. , identical decomposition of applied C 3 and C 4 sugars in soil, was investigated and proven. The relative contribution to the CO 2 efflux was higher, but shorter with an increased (microbial) availability of the C source, i.e. , sugar > slurry > SOM. The shortcomings and limitations as well as possible future applications of the suggested method are discussed.