Moderate grazing increased alpine meadow soils bacterial abundance and diversity index on the Tibetan Plateau

The response of grassland soil bacterial community characteristics to different grazing intensities are central ecological topics. However, the underlying mechanisms between bacterial abundance, diversity index, and grazing intensity remain unclear. We measured alpine meadow soil bacterial gene richness and diversity index under four grazing intensities using 16S rDNA sequence analysis on the Tibetan Plateau. The results suggest that extreme grazing significantly decreased alpine meadow both bacterial gene abundance and diversity index (P<0.05). The lowest operational taxonomic unit numbers were 3012 ± 447 copies under heavy grazing in the growing season. It was significantly lower than heavy grazing with approximately 3958 ± 119 copies (P<0.05). The Shannon index for medium and high grazing grassland bacterial diversity was slightly higher than for light grazing in the growing season. Furthermore, the lowest index was approximately 9.20 ± 0.50 for extreme grazing of grassland in the growing season. The average bacterial gene abundance and diversity index in the dormancy period was slightly higher than that in the growing season. Soil bulk density, pH, ammonium and nitrate nitrogen were the main positive factors driving grazed grassland bacterial communities. Our study provides insight into the response of alpine meadows to grazing intensity, demonstrating that moderate grazing increases bacterial community diversity in grazed grasslands.

草原土壤细菌群落特征对不同放牧强度的响应是核心生态学研究议题。然而，细菌丰度、多样性指数与放牧强度之间的潜在作用机制仍未明晰。本研究在青藏高原采用16S rDNA（16S核糖体DNA）序列分析技术，测定了四种放牧强度下高寒草甸的土壤细菌基因丰富度与多样性指数。研究结果显示，极端放牧会显著降低高寒草甸的土壤细菌基因丰度与多样性指数（P<0.05）。生长季重度放牧样地的操作分类单元（operational taxonomic unit, OTU）数量最低，为3012 ± 447拷贝，该数值显著低于约3958 ± 119拷贝的放牧样地（P<0.05）。生长季中牧与高牧草地的细菌多样性香农指数（Shannon Index）略高于轻牧草地；而极端放牧草地的香农指数最低，生长季约为9.20 ± 0.50。休眠期的土壤细菌基因丰度与多样性指数平均值略高于生长季。土壤容重、pH值、铵态氮与硝态氮是驱动放牧草地细菌群落的主要正向调控因子。本研究揭示了高寒草甸对放牧强度的响应规律，证实适度放牧可提升放牧草地的细菌群落多样性。