The procedure to extract the microbial substrate and inoculate it into the experimental chambers was based on Scott-Fordsmand et al. (2008). Freshly collected soil from the control area of the field site (1 kg wet weight) was mixed with 2 l of deionized water and shaken for 3 h. After this, the soil–water solution was filtered through a 50 m mesh and diluted 10 times for use in the experiment. The soil water content was adjusted to 20% of which 10% was added with the microbial inoculate.