design: Genomic DNA was extracted from the samples using the respective DNA extraction kits (e.g., MOBIO PowerSoil DNA Isolation Kit). The V4 region of the 16S rRNA gene was amplified using primers 515F (5'-GTGCCAGCMGCCGCGGTAA-3') and 806R (5'-GGACTACHVGGGTWTCTAAT-3') with Premix Taq (Takara) under the following PCR conditions: 94C for 5 min; 30 cycles of 94C for 30s, 52C for 30s, and 72C for 30s; followed by a final extension at 72C for 10 min. PCR products were pooled based on equal mass after concentration measurement with GeneTools software, and target fragments were purified by gel excision using the E.Z.N.A. Gel Extraction Kit. Sequencing libraries were prepared using the ALFA-SEQ DNA Library Prep Kit, and library quality was assessed on a Qsep400 system and Qubit 4.0. Finally, paired-end 250 bp (PE252) sequencing was performed on an Illumina NovaSeq platform.