design: The total DNA of each sample was extracted from 0.25 g soil using the Fast DNA SPIN for Soil. Each sample triplicate amplification, and electrophoresis was used to verify positive PCR products. Amplicons from triplicate reactions were purified using the AxyPrepDNA Extraction Kit (AXYGEN Company) and mixed in equal density ratios. Sequencing was carried out on an Illumina Miseq platform (2  377 bp paired-end reads).