Total microbial DNA was extracted from approximately 0.1g of soil per sample using the PowerSoil DNA Isolation Kit (QIAGEN, Hilden, Germany), following the manufacturers instructions strictly to ensure the purity and representativeness of the extracted DNA. The V3V4 region of the bacterial 16S rRNA gene was amplified using specific primers 338 F and 806R, both containing Illumina adapter sequences. PCR products were verified by agarose gel electrophoresis, purified using a purification kit, and then subjected to library preparation.