锦鸡儿属与黄芪属植物主要生长于荒漠土壤中，这两种豆科植物根部所形成的根瘤可为其生长提供良好的氮素营养。能够与其形成根瘤的主要为中慢生根瘤菌属，其次为根瘤菌属，这些根瘤菌长期在土壤中营腐生生活，基因组上的持家基因、生态环境相关基因、共生固氮相关基因等都会发生遗传分化与基因交流，进而形成了不同的生物地理分布规律以及不同的种群。尽管如此，有的共生基因、分泌系统、氢化酶系统的一些基因在进化过程中仍然具有一定的保守性，这为深入探讨中慢生根瘤菌的分子进化历程提供了参考资料。

Chapter Ⅰ Genetic divergence and gene flow among Mesorhizobium
strains nodulating the shrub legume Caragana growing
along the semi-fixed desert belt in north China
Introduction
Materials and methods
Results
Discussion
Conclusion
Chapter Ⅱ Biogeographic distribution of rhizobia associated with
the medicinal legumes Astragalus spp. and Hedysarum
polybotrys in agricultural soils
Introduction
Materials and methods
Results
Discussion
Chapter Ⅲ Evolutionarily conserved nodE, nodO, T1 SS, and
hydrogenase system in rhizobia of Astragalus
membranaceus and Caragana intermedia
Introduction
Materials and Methods
Results
Discussion
Conclusion
Chapter Ⅳ Genetic divergence among Bradyrhizobium strains
nodulating wild and cultivated Kummerowia spp.
in China
Introduction
Materials and Methods
Results
Discussion
Conclusion
References