Soil microbial biomass and respiration measurements
We measured soil microbial biomass (Cmic) and respiration using 5 g of fresh soil on an automated O2-micro-compensation apparatus (Scheu 1992). Soil microbial respiration was measured first, as the oxygen consumption per hour per dry weight of soil in µl (respiration given in µl O2 g-1 dry weight h-1). This reflects the active part of the soil microbial community at the sampling time. Afterwards, the microbial biomass (given in µg microbial carbon g-1 dry weight) was measured by adding glucose (8 mg per gram of dry soil) to the samples (substrate-induced respiration [SIR] method). This measurement represents the total metabolically active biomass of soil microorganisms of the sample.