The 16S V4 and ITS1 region amplification of all samples was respectively performed by the universal primers 515F (5′-GTGCCAGCMGCCGCGGTAA-3′) - 806R (5′-GGACTACH VGGGTWTCTAAT-3′) and ITS1F (5′-CTTGGTCATTTAGAGGAAGTAA-3′) - ITS2 (5′- GCTGCGTTCTTCATCGATGC-3′) with the barcode on ABI GeneAmp® 9700 PCR instrument (Caporaso et al., 2012 (link); Huang et al., 2015 (link)). After mixing and detecting with 2% agarose gel electrophoresis, the PCR products were recycled and purified with Agencourt AMPure Beads (Beckman Coulter, Indianapolis, IN). Finally, the PCR products were quantified using Quant-iT PicoGreen dsDNA Assay Kit and then mixed in proportion according to the concentration of each sample.
PCR amplicon libraries were generated by an Illumina TruSeq Nano DNA LT Sample Prep Kit (FC-121-4001). The library quality was then assessed and amplicon sequencing was performed on an Illumina HiSeq 2500 platform, generating 2 ×300 bp sequences. All raw data were submitted to the Sequence Read Archive (SRA) database with the accession numbers