A plant growth-promoting rhizobacterium ( PGPR) was screened from plant rhizospheric soil by the bioassay methods of wheat leaf green retaining and radish cotyledon growth and isolated,and then,the PGPR was identified with molecular biology means. A pot experiment of Platycladus orientalis was conducted with controlled water supply ( control, light drought stress,moderate drought stress and severe drought stress) and the PGPR was inoculated. Effects of the plant growth-promoting rhizobacteria on dry weight,antioxidant enzyme,and endogenous hormone of P. orientalis was studied in the present research. According to the morphologic characteristics,physiological biochemical properties and phylogenetic analysis of 16S rRNA genes,the PGPR isolated in the present study was identified as Bacillus cereus. Under well-watered conditions,there was little effect of PGPR inoculation on antioxidant enzyme,osmotic adjustment substance,and lipid peroxidation products of P. orientalis. Under drought stress conditions,B. cereus inoculation increased the antioxidant enzyme activities. However,osmotic adjustment substance,and lipid peroxidation products were decreased as a result of PGPR inoculation. Regardless of the water status,the contents of indoleacetic acid,gibberellins,and zeatin in P. orientalis were significantly increased as a result of B. cereus inoculation. Besides,PGPR decreased abscisic acid content by 23. 81% under severe drought stress. The dry matter accumulation of P. orientalis was significantly improved due to B. cereus inoculation. Additionally,B. cereus inoculation promoted shoots dry matter accumulation of P. orientalis,however, it had a decreasing effect on roots dry mass accumulation with the increasing drought intensity. The results suggest that B. cereus inoculation could effectively alleviate the damage of drought stress to P. orientalis by regulating the antioxidant enzyme and osmotic adjustment substance,and stimulating some endogenous hormone production. In summary,PGPR inoculation could improve drought resistance of P. orientalis,and improve the shoot dry matter accumulation,and it would be a supplementary measure for afforestation in arid and semi-arid environment.%从植物根际土壤中筛选出1株植物根际促生细菌( PGPR)，并对其进行分子生物学鉴定。在盆栽试验条件下，以侧柏为材料，研究接种 PGPR在4个水分梯度(正常浇水、轻度干旱、中度干旱和重度干旱)下对侧柏生理生态特征及生长的影响。通过形态学观察、生理生化测定、16S rDNA基因测序及系统发育树分析，筛选出的 PGPR鉴定为蜡样芽孢杆菌。正常浇水的情况下，接种蜡样芽孢杆菌对侧柏抗氧化酶、渗透调节物质和膜脂过氧化产物的影响较小；随着干旱胁迫强度的增加，接种蜡样芽孢杆菌可显著增加抗氧化酶活性，但显著降低渗透调节物质和膜脂过氧化产物的积累。接种蜡样芽孢杆菌均可不同程度地提高侧柏生长素、赤霉素和玉米素的含量。正常浇水和轻度干旱时，接种蜡样芽孢杆菌显著提高脱落酸含量，而重度干旱时 PGPR 处理的脱落酸含量降低23.81%。此外，接种蜡样芽孢杆菌显著增加侧柏干物质积累，且随着干旱胁迫强度的增加，对根系干物质积累的影响越来越小，而对地上部的影响越来越大。综合分析认为，干旱生境下接种植物根际促生细菌，侧柏能够通过调节保护酶活性和渗透调节物质含量，促进一些激素类物质的产生来减轻干旱对植物生长造成的伤害，促进干物质积累。
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