Abstract: In order to enhance the capacity of nodulation and nitrogen fixation of Cassia (Chamaecrista spp.),and to further promote its application and extension in acidic soils,Chamaecrista rotundifolia and Chamaecrasta nictitans were used in this study to screen effective rhizobial strains. 10 candidate rhizobial strains were isolated from the nodules of Cassia pastures from acid soils through isolation,purification,nodA gene identification,etc. The results from 16S rDNA gene sequencing and phylogenetic tree analysis showed that all these 10 rhizobial strains belonged to bradyrhizobium sp. Moreover,the re-inoculation experiment indicated that all the 10 candidate rhizobial strains were able to establish symbiosis with Cassia rotundifolia to form nodules. Compared with non-inoculated plants,the nitrogenase activity was 0.08~4.65 mol·g^-1·h^-1,and the dry weight,SPAD value and nitrogen content of the plants increased by 99.17%~372.14%,399.27%~789.05%,and 235.00%~1043.33%,respectively. Among them,4 rhizobial strains including TXR2,TXN1,WYSR1 and JYN6 displayed the largest contribution to the improvement of nitrogen nutrition in Cassia rotundifolia,and the symbiosis of TXN1 and host plant could produce the largest number of nodules while the highest nitrogenase activity was found after inoculation with JYN6. These results suggest that 4 effective rhizobial strains were isolated and identified,which has great application prospects.

Key words: Cassia pasture, Acidic soils, Rhizobia, Isolation, Identification

摘要： 为提高豆科决明属（Chamaecrista spp.）牧草的结瘤能力和固氮效率，促进决明属牧草在酸性土壤中的应用及推广，本研究以圆叶决明（Chamaecrista rotundifolia）和羽叶决明（Chamaecrasta nictitans）为试验材料，通过分离、纯化、nodA基因鉴定等方法，从酸性土壤里决明属牧草的根瘤中分离到10株候选根瘤菌株系。16S rDNA测序及系统发育树分析表明，这10株根瘤菌均属于慢生型根瘤菌。回接试验表明，上述10株根瘤菌均能与圆叶决明共生，形成根瘤。与不接种的对照相比，其固氮酶活性为0.08~4.65 μmol·g^-1·h^-1，植株干重、SPAD值和氮含量分别提高了99.17%~372.14%，399.27%~789.05%，235.00%~1043.33%。其中，4株根瘤菌TXR2，TXN1，WYSR1，JYN6对圆叶决明氮营养贡献最大，并且TXN1与宿主共生形成的根瘤数目最多，而JYN6的固氮酶活性最高。说明本研究分离鉴定到4株决明高效根瘤菌，具有较好的应用前景。

关键词: 决明属牧草, 酸性土壤, 根瘤菌, 分离, 鉴定