Abstract: In order to obtain the strains of symbiotic rhizobium of Medicago polymorpha L. with strong acid and aluminum resistance, five nodule samples collected from different regions were isolated, purified and identified. The identified rhizobia were studied for bacterial morphological observation, low nitrogen backconnection, acid resistance and aluminum resistance. The results showed that YS-8, YS-10, DH-9 and DH-31 belonged to Rhizobium sp, CX-44 belonged to Sinorhizobium medicae, and the five strains all conformed to the basic morphological characteristics of rhizobia. After inoculation with 5 rhizobia strains, the dry weight, fresh weight, plant height and nodulation number of Medicago polymorpha L. were significantly higher than those in the control;In the range of 7.5~4.5 pH, all 5 strains growed normally, and when pH was 3.5, all 5 strains died;When Al³⁺ concentration was between 100~1 500 mg·L^-1, the growth of the strains gradually slowed down as the Al³⁺ concentration increased, and when the Al³⁺ concentration reached 2 000 mg·L^-1, all 5 strains died. The isolated five rhizobia strains could coexist with Medicago polymorpha L. and promote their growth, and had strong acid aluminum resistance. The five screened strains of rhizobia could be popularized and used under the condition of pH greater than 3.5 and aluminum ion concentration (pH=5) less than 1 500 mg·L^-1, and the strain CX-44 was the best.

Key words: Acidic soil, Medicago polymorpha L., Symbiotic rhizobia, Acid-fast aluminum strains

摘要： 为了获得耐酸铝性强的楚雄南苜蓿（Medicago polymorpha L.）共生根瘤菌菌株，本研究对从不同地区采集到的5份根瘤样品进行分离、纯化和鉴定。对鉴定得到的根瘤菌进行菌体形态观察、低氮回接以及耐酸、铝特性的研究。结果表明：YS-8，YS-10，DH-9，DH-31属于根瘤菌属根瘤菌、CX-44属于中华根瘤菌属苜蓿中华根瘤菌，5个菌株均符合根瘤菌基本形态特征。接种5株根瘤菌后，楚雄南苜蓿的干重、鲜重、株高、结瘤数均显著高于对照（P<0.05）；pH值在4.5~7.5范围内，5株菌株均能正常生长，当pH值=3.5时，5株菌株全部死亡；当Al³⁺浓度在100~1 500 mg·L^-1之间，随着Al³⁺浓度的升高，菌株生长逐渐缓慢，Al³⁺浓度达到2 000 mg·L^-1时，5株菌株全部死亡。分离出的5株根瘤菌均能与楚雄南苜蓿共生结瘤并促进其生长，且具有较强的耐酸铝性。筛选出的5株根瘤菌均能在pH值大于3.5且铝离子浓度（pH值=5）小于1 500 mg·L^-1的条件下推广使用，菌株CX-44的效果最佳。

关键词: 酸性土壤, 楚雄南苜蓿, 共生根瘤菌, 抗酸铝菌株