Abstract:

In order to understand the community structure of rhizosphere diazotrophs at different developmental stages of sand-fixing pioneer plant Agriophyllum squarrosum， the rhizosphere soil at seedling stage， vegetative stage， reproductive stage and withering stage in Hobq Desert was taken as the research object. The composition and diversity of diazotrophs community at different developmental stages were analyzed by high-throughput sequencing， and the correlation between diazotrophs community and soil nutrients was analyzed by redundancy. The results showed that β-Proteobacteria and Azohydromonas were the main diazotrophs groups in the rhizosphere of A. squarrosum， which have the characteristics of rapid growth and autotroph， with abundance ranging from 44.30% to 90.51% and 35.05% to 72.89%， respectively. There were significant differences in rhizosphere diazotrophs communities at different developmental stages， the different diazotrophs species were Azohydromonas， Skermanella and Bradyrhizobium at genus level. In the vegetative stage， the relative abundance of Skermanella positively correlated with organic matter， neutral phosphatase activities and neutral protease activities was significantly higher than that in seedling stage （2.76 times）， reproductive stage （4.22 times） and withering stage （3.13 times）. In the reproductive stage， the relative abundance of Bradyrhizobium negatively correlated with organic matter， neutral phosphatase activities， available phosphorus and catalase activities was significantly higher than that in seedling stage （3.56 times） and withering stage （8.58 times）， and did not appear in the vegetative stage. Organic matter， sucrase activities involved in carbon cycle and available nitrogen， urease， neutral protease involved in nitrogen cycle were significantly increased at the seedling and the vegetative stages， rhizosphere nutrients decreased significantly during the reproductive stage. In conclusion， the rhizosphere diazotrophs communities of A. squarrosum had significant differences at different developmental stages. Diazotrophs in seedling stage and vegetative stage of A. squarrosum mainly accumulated carbon and nitrogen sources， and the reproductive stage mainly consumed nutrients， which promoted the nutritive competitive succession of rhizosphere diazotrophs， this study provides a theoretical basis for the restoration of pioneer plant population and the application of nitrogen fertilizer in sand industry.

Key words: Agriophyllum squarrosum, developmental stage, diazotrophs, succession, enzyme activity