Abstract: In order to enhance the drought tolerance of Medicago sativa L. ‘Xinmu 1’, Bacillus atrophaeus WL520 was isolated from the rhizosphere of Nitraria tangutorum grown in the arid sandy land of Wulan, Qinghai Province, and then irrigated Alfalfa. The biological activity of the strain was determined. The antagonistic activity, antibacterial enzyme activity, the drought tolerance, IAA production and nitrogen fixation activity of the strain were measured. Molecular identification of the strain was conducted by 16S rDNA and gyrB gene sequencing. The growth-promoting effect of the strain on Medicago sativa under drought stress was determined. The results showed that the strain WL520 exhibited antagonistic activity against pathogens, produced four antibacterial hydrolytic enzymes, showed strong drought tolerance, IAA production and nitrogen fixation ability, and was identified as Bacillus atrophaeus. Compared with drought stress without the strain, after root irrigation with the bacterial suspension of strain WL520, the plant height, root length and fresh weight of Medicago sativa increased, the chlorophyll and SOD content increased, and the MDA content decreased, indicating that strain WL520 had a significant growth-promoting effect on Medicago sativa under drought stress. This study provided excellent strains and theoretical basis for the exploration of highland microbial resources and growth promoting of pasture.

Key words: Bacillus atrophaeus, Biological activity, Drought stress, Alfalfa

摘要： 为增强紫花苜蓿‘新牧1号’（Medicago sativa L.‘Xinmu 1’）的耐旱性，以分离筛选自青海乌兰干旱沙地白刺（Nitraria tangutorum）根际的萎缩芽孢杆菌（Bacillus atrophaeus）WL520对紫花苜蓿进行灌根处理，并测定菌株生物活性。通过平板对峙、透明圈法测定菌株拮抗、抑菌酶活性；测定菌株耐旱性及产IAA、固氮活性；采用16S rDNA及gyrB基因测序对菌株进行分子鉴定；并测定干旱胁迫下，菌株促紫花苜蓿的生长效应。结果表明：菌株WL520对2种病原真菌表现出拮抗活性，可产生4种抑菌水解酶；并表现出较强耐旱性、产IAA及固氮能力；分子鉴定为萎缩芽孢杆菌（Bacillus atrophaeus）。与干旱胁迫（D）相比，菌液灌根（DB）后，紫花苜蓿株高、根长及鲜重提高，叶绿素及SOD含量提高，MDA含量下降。因此，干旱胁迫下，菌株WL520对紫花苜蓿具有显著促生效应，本研究为挖掘高原微生物资源及促牧草生长提供了优异菌株及理论基础。

关键词: 萎缩芽孢杆菌, 生物活性, 干旱胁迫, 紫花苜蓿