西藏岗巴拉山土壤细菌多样性海拔分布格局及其驱动因子

高原山地是对全球气候变化最为敏感的脆弱生态系统之一，研究高原山地土壤细菌群落沿海拔变化特征，对于揭示受气候变化和人为干扰的山地微生物群落结构和功能有十分重要的科学意义。研究以西藏岗巴拉山作为研究对象，运用Illumina MiSeq高通量测序技术，基于精细样方尺度分析了岗巴拉山沿海拔梯度土壤细菌群落组成和多样性的变化特征及其驱动因子。结果表明：岗巴拉山土壤细菌共包含36门125纲307目477科838属1878种，将12个海拔带分为高中低3组（低海拔从3800-4100 m、中海拔从4200-4500 m、高海拔从4600-4900 m），中海拔总分类操作单元（OTU）数最多，特有OTU数最少，土壤细菌群落丰富度随海拔升高呈单峰趋势，但其特异性随海拔呈U型分布格局。岗巴拉山土壤细菌群落中的优势菌门是放线菌门、酸杆菌门、变形菌门、绿弯菌门、疣微菌门和芽单胞菌门等，土壤细菌群落Shannon多样性指数随海拔升高而逐渐减小，而Simpson多样性指数在高海拔最高，Chao指数随海拔升高呈单峰变化趋势。主坐标分析（PCoA）表明土壤细菌群落结构在不同海拔梯度上存在显著差异，且低海拔土壤细菌群落组内也存在显著差异。冗余分析（RDA）表明海拔、pH、总氮、总磷和有机碳对土壤细菌群落结构有显著影响，与环境因子相关性分析表明海拔、pH、总氮、总磷和有机碳与土壤细菌群落结构显著相关，曼特尔检验表明pH和海拔是影响土壤细菌群落的关键因素。岗巴拉山土壤细菌多样性沿海拔梯度呈单调下降趋势，pH是影响土壤细菌群落沿海拔变化特征的关键环境因子，总氮、总磷和有机碳也是影响土壤细菌群落的重要环境因子。

Elevation distribution pattern and driving factors of soil bacterial diversity on Mount Gangbala, Xizang, China

Plateau mountains are one of the most sensitively fragile ecosystem to global climate change. Studying the characteristics of plateau mountain soil bacterial communities along the elevational gradient is of great scientific significance for revealing the structure and function of mountain microbial communities affected by global change. In this study, the characteristics and driving factors of soil bacterial community composition and diversity along the elevational gradient on the Mount Gangbala were analyzed based on the fine quadratic scale by using Illumina MiSeq high-throughput sequencing technology. The results showed that the soil bacteria of Mount Gangbala contained a total of 36 phyla, 125 classes, 307 orders, 477 families, 838 genera, and 1878 species. The 12 elevation belts were divided into 3 groups of low, middle and high (low altitude 3800-4100 m, middle altitude 4200-4500 m, high altitude 4600-4900 m). The total Operational Taxonomic Unit (OTU) number at middle altitude was the largest, but the number of unique OTU at middle altitude was the least. The richness of soil bacterial communities showed a unimodal trend with the increase of altitude, but the specificity of soil bacterial communities showed a U-shaped distribution pattern with the increase of altitude. The dominant phyla of the soil bacterial community in the Mount Gangbala are Actinobacteriota, Proteobacteria, Acidobacteriota, Chloroflexi, Verrucomicrobiota, Gemmatimonadota, etc. The Shannon diversity index of soil bacterial community gradually decreased with the increase of altitude, and was lowest at high altitude; while the Simpson diversity index was highest at high altitude, and the Chao index showed a unimodal trend with the increase of altitude. Principal co-ordinate analysis (PCoA) showed that there were significant differences in soil bacterial community structure along the altitude gradient, and there were also significant differences within the low-altitude soil bacterial community group. The redundancy analysis (RDA) showed that altitude, pH, total nitrogen, total phosphorus, and organic carbon had significant effects on soil bacterial community structure. Correlation analysis with environmental factors showed that altitude, pH, total nitrogen, total phosphorus, and organic carbon were significantly correlated with soil bacterial community structure. Mantel test showed that pH and altitude were the critical factors affecting soil bacterial community. Soil bacterial diversity on the Mount Gangbala showed a monotonous decreasing gradient along the elevation gradient, while pH was the key environmental factor affecting the characteristics of soil bacterial changes along the elevational gradient, and total nitrogen, total phosphorus and organic carbon were also important environmental factors affecting soil bacterial community.