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 V4 primers 515F/806R (Walters et al. 2015) followed by Illumina NextSeq sequencing preparation with the Reagent Kit (500-cycles).