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Soil plays a crucial role in global climate change, e.g. soils in afforested areas have a high potential of carbon(C) sequestration. Furthermore, tree species identity affects soil microbial biomass (SMB) and community structure.Recent findings on soil organic matter (SOM) revealed that soil microorganisms are not only crucial for SOM formationthrough plant litter degradation but SMB may also directly contribute to SOM and its composition. However, the role andinteractions of litter quality, microbial turnover and composition of SMB and SOM remain unclear. Hence, soil profiles(organic forest floor and mineral soil layers) at a recultivated and afforested post-mining site were investigated to evaluatethe influence of litter quality provided by different tree species (Fagus sylvatica, Pseudotsuga menziesii, Pinus nigra) andsoil depth – representing different degrees of organic matter (OM) turnover – on the molecular composition of chloroformfumigation extracted SMB-derived compounds in comparison with easily extractable (non-fumigated) SOM-derivedcompounds. The SMB extracts were analyzed for microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus(MBP). The molecular composition of SMB and SOM compounds were determined by electrospray ionization Fouriertransformation ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) complemented by the determination of ninemonosaccharides representing microbial or plant origin.Van Krevelen diagrams obtained from the ESI-FT-ICR mass spectra revealed the substantial contribution of microbialderivedcompounds to extractable SOM that further increased with soil depth. Analysis of the easily extractablemonosaccharides implied that >99% were of microbial origin. Microbial sugars as well as MBC, MBN and MBP explainedbest depth-related variations of extractable SMB compounds indicating that supply and availability of C-rich OM drivethese parameters. Furthermore, the contribution of microbial sugar C to MBC increased with depth, suggesting thatrecycling of carbohydrates is ...