BETA-FOR_SP4_Soil microbial activity and biomass_2018-2022

Samples were taken each year around 1st of October. We took four soil cores per patch (5cm diameter, 10 cm depth), pooled these per patch and sieved them at 2mm. We used an automated O2 microcompensation system (Scheu, 1992) to assess basal respiration and microbial biomass. Basal respiration represents the mean oxygen consumption per hour (µl O2 h-1 g soil dw-1) without any substrate addition. This indicates the active portion of the soil microbial community at the time and soil condition of sampling. For this, the mean oxygen consumption between the hours 10-20 was taken. Microbial biomass carbon was determined through substrate-induced respiration, which measures the respiratory response of microorganisms to added glucose and water. An aqueous solution containing 8 mg of glucose per gram of dry soil was added. The lowest substrate-induced respiration observed over three consecutive hours within the first 10 hours was taken as the maximum initial respiratory response (MIRR), taking place before microbial growth started. Microbial biomass (µg C g-1 soil dw) was calculated as 38 x MIRR (Beck et al., 1997). This method measures the full potential of the living microbes that can use glucose. The respiratory quotient is calculated by dividing the basal respiration by the microbial biomass. It determines the ratio of built up carbon to investment in respiration. If the respiratory quotient is low, carbon use is efficient, as more microbial biomass can be built up with less respiration. Soil water content was determined by weighing the fresh sample, drying it at 75°C for three days, and reweighing it. The percentage of water in the fresh sample was calculated and used as the measure of soil water content.It is recommended to use device as a random effect in models when analyzing the data because the different devices might measures slightly different.