d13C was measured on the Euro EA Elemental Analyzer (Eurovector, Milan, Italy) unit with a
ConFlo III interface (Thermo-Fischer, Bremen, Germany) and the
Delta V Advantage IRMS (Thermo Fischer, Bremen, Germany). 13C
uptake into fumigated and unfumigated extracts was calculated
according to the mixing model Eqs. (1) and (2) and microbial
biomass C and for13C incorporation, an extraction factor of 0.45 was
applied according to Wu et al. (1990).