16S and amoA genes amplicons from nitrifying soil microorganisms
The total concentration of microbial DNA was measured using the Qubit High Sensitivity assay (Thermofisher) and normalized at 1 ng/l prior to PCR amplification. The amplification were carried out using amoA1F/amoA2R (Rotthauwe et al., 1997) primer followed by Illumina NextSeq sequencing preparation with the Reagent Kit (500-cycles).