Abstract: In this study， the effects of different grazing intensities on the composition and diversity of soil bacterial communities in desert steppe were investigated. Three grazing intensities，light grazing （LG）， moderate grazing （MG） and heavy grazing （HG），were set up， and no grazing area （CK） was as control. High-throughput sequencing of 16S rRNA sequences of soil bacteria at the base of biological crusts， bare land and dominant species （Stipa breviflora and Cleistogenes songorica） was carried out to analyze the effects of grazing intensity on soil bacterial composition and Alpha diversity in different microhabitats. The results showed that： （1） Actinobacteria， Proteobacteria， Chloroflexi and Acidobacteria were the dominant bacteria at the phylum level， and Rhodobacter， Microcladium， RB41， Sphingomonas and Segetibacter were the dominant bacteria at the genus level. （2） Different grazing intensities had no significant effect on the ACE index， Chao1 index and Shannon index of soil bacteria in different microhabitats. The Simpson indexes of Stipa breviflora basal soil and Cleistogenes songorica basal soil were significantly higher than those of biological crusts （P<0.05）. （3） The results of RDA analysis showed that total carbon， total nitrogen， total phosphorus， TC/TN ratio， pH value and soil moisture were the driving factors of the changes of soil bacterial α diversity. These results would provide scientific guidance for achieving sustainable management of desert steppes.

Key words: Grazing, Desert grassland, Microhabitat, Soil bacterial community, Structure

摘要： 本研究以荒漠草原为研究对象，探究不同放牧强度对其微生境土壤细菌群落组成和多样性的影响。设置轻度放牧（LG）、中度放牧（MG）和重度放牧（HG）三个放牧强度，无放牧区（CK，作为对照），并对生物结皮、裸地、优势种[短花针茅（Stipa breviflora，SB）、无芒隐子草（Cleistogenes songorica，CS）]基部土壤细菌16S rRNA序列进行高通量测序，从而分析放牧强度对不同微生境土壤细菌组成、Alpha多样性的影响。结果显示：（1）细菌门水平均以放线菌门、变形菌门、绿弯菌门和酸杆菌门为优势菌门，细菌属水平均以红色杆菌属、微枝形杆菌属、RB41、鞘鞍醇单胞菌属及Segetibacter为优势菌属。（2）不同放牧强度对不同微生境土壤细菌的 ACE指数、Chao1 指数和 Shannon 指数无显著影响，短花针茅基部土壤及无芒隐子草基部土壤的 Simpson 指数均显著高于生物结皮（P<0.05）。（3）RDA分析结果表明，全碳、全氮、全磷、碳氮比、pH值和土壤湿度是驱动土壤细菌α多样性变化的环境因子。本研究揭示了放牧通过改变不同微生境土壤理化因子来影响荒漠草原土壤细菌群落构成，该成果为实现荒漠草原的可持续管理提供科学指导。

关键词: 放牧, 荒漠草原, 微生境, 土壤细菌群落, 结构