Decomposition of 14C- and 15N-labelled microbial cells in soil

To obtain detailed information on the quantities and characteristics of nitrogen derived from mineralizing dead microbial biomass in soil, ¹⁴C- and ¹⁵N-labelled microorganisms, i.e. three eukaryotic (fungal) species, two prokaryotic species or their mixture (eukaryotic to prokaryotic cells = 8:2), were grown in vitro, dried, ground and added to parabrown earth and chernozem soils, respectively. The mean percent of ¹⁴C decomposition of labelled microorganisms obtained after 10 days was 43 ± 6.3% for parabrown earth and 34 ± 4.0% for chernozem soil. About 50% of the C in the dead microorganisms was mineralized during the first 28 days of incubation. About 76% of the flush of soil organic N mineralization within 28 days, which was caused by the drying-rewetting treatment, was derived from dead microbial biomass in soil. About 33% of the added dead microbial-¹⁵N was mineralized in parabrown earth soil during 28 days of incubation and about 37% of newly immobilized ¹⁵N during the decomposition of added microorganisms was mineralized during the 28 days following a dryingrewetting treatment.