The V3-V4 hypervariable regions of 16S rRNA genes were amplified using a universal forward sequencing primer and a uniquely barcoded reverse sequencing primer to allowmultiplexing. Amplicon sequencing was conducted on the Illumina HiSeq platform, generating 250 bp paired-end raw reads. Raw data were first merged and filtered to obtain clean data. Chimeric sequences were detected and removed to obtain effectivedata. Effective data were grouped by 97% DNA sequence similarity into operational taxonomic units (OTUs), with low abundance OTUs (<0.005%) removed. OTUclustering and species annotation were performed, and the relative species evenness and abundance distribution were analyzed. OTU picking, taxonomic assignment, andconstruction of phylogenetic trees.