Microbial transformations are key processes of soil organic matter (SOM) formation, stabilization and
decomposition. Combination of position-specific 13C labeling with compound-specific 13C-PLFA analysis
is a novel tool to trace metabolic pathways. This combination was used to analyze short-term transformations
(3 and 10 days after tracer application) of two key monosaccharides: glucose and ribose in
soil under field conditions. Transformations of sugars were quantified by the incorporation of 13C from
individual molecule positions in bulk soil, microbial biomass (by CFE) and in cell membranes of microbial
groups classified by 13C-PLFA.