Resource Of Symbiotic Nitrogen-Fixation Of Legume And Diversity Of Rhizobia In Karst Shrub Communities

The rocky desertification of Karst region is serious and the ecosystem becomes serious degradation. The Karst region is one of the ecologically fragile areas in China, which is urgent to-treatment. In the region, nitrogen drain is serious in farming and degraded soils, which makes nitrogen becoming one of the important limiting factor to recover the vegetation. Legumes can significantly improve the structure of the soil, nutritional status, and the microenvironment of the soil, which can create the conditions for other plants migration, settlement and growth. Thus it can promote the succession and restoration of degraded ecosystem. But so far, the survey of the Karst areas about leguminous plants and their symbiotic rhizobial resources is little, the regional specificity of rhizobium and its ecological effect is unclear. In addition, during the restoration of degraded ecosystems and in the processing of controlling the rocky desertification, the shrub community stage is important. The area of shrub communities is largest on the light, moderate and severe degree of rocky desertification region. The erosion of soil and other degradation processes in ecosystems stop, and the fertility of soil and the diversity of species increase significantly, and the recovery ability of shrub community gradually strengthen on the stage of shrub communities. The research about the legumes and their symbiotic rhizobial resource in Karst areas can helps us to deepen the understanding of the diversity of the regional legumes and the specificity of and rhizobia symbiosis resource. It can provide the technical guidance for selecting the pioneer legumes-efficient nitrogen-fixing rhizobium combinations which can adapt to Karst degraded ecosystem, and provide a theoretical basis for the application of leguminous plants to Karst ecological recovery and reconstruction.In this research, we investigated the vegetation of25shrub communties and collected the nodules of legume plants in Karst shrub communities, then constructed the phylogenetic trees based on16S rDNA and nifH sequences of the rhizobia. The main results of my research were shown as following: There are81families,172genera,218species of plants in plots. The largest family is Leguminosae. In shrub layer, the dominant species of shrub communities are Loropetalum chinense, Vitex negundo, Litsea coreana var. sinensis. In herbaceous layer, the dominant species of shrub communities are Selaginella uncinata, Nephrolepis cordifolia, Carex tristachya. Compared to the dominant species, the important values of legume plants are very small. Of sixteen legume plants,Six species of Fabaceae and one species of Mimosaceae can nodulate in total sixteen legume species. The forms of the most nodules are spherical or rod-like. The color of the most nodules is khaki or brown. The most nodules grow on the lateral roots. Seven strains are isolated. The colony morphology of the strains in YMA are transparent or translucent, white or milk white, convex, edge smooth. The strains are Gram negative strains.The phylogenetic trees based on16S rDNA and nifH sequences are constructed by neighbour-joining method. All of the seven strains belong to Bradyrhizobium, but there are some differences between the phylogenetic trees based on16S rDNA and nifH sequences.