Characterisation of the microbial biomass in lignite-containing mine soils by radiocarbon measurements

A method of sample preparation is presented which allows for the characterisation of the soil microbial biomass by 14C activity measurements at natural abundance of 14C. By the use of freeze-drying instead of chloroform for the disruption of microbial cells, the possible contamination of the sample by 14C is avoided. Our data show a close relationship between the two methods. After extraction by CaCl2 the 14C activity of the freeze-dried labile carbon was recorded by accelerator mass spectrometry. Our data for lignite-containing mine soils indicate that lignite carbon which does not show 14C activity is incorporated in the soil microbial biomass. The method can thus be used to follow microbial degradation of fossil carbon (e.g. lignite) in soil.