| Biological soil crusts (BSC) play an important role in defending desert, because of the presence of soil microorganism in the BSC, which shows strong adaptability and viability, and has an important effect on forming of BSC, including transformation of soil organic matter, soil fertility improvement and keeping balance of soil ecosystem. Microorganism has a consanguineous correlation with soil and plants. In the study, we investigated content of soil microorganism, soil microbial biomass (MB), soil enzyme activity and nutrients content in root soil of Artemisia ordosica, and analyzed the effect of microorganism on generation and development of BSC (moss crusts and algae crust) and livingness of A. ordosica under different soil and climate conditions in Kubuqi Desert. The research may provide the academic and practice basis for planting of artificially BSC and rebuilding of hungriness vegetation.The main results are as follows:1. Nutrients content in soil covered with moss crusts was evidently higher than that in no-crust soil. The result showed that BSC had obvious effect on accumulation of nutritional elements and ameliorating of leanness desert. 2. The amount of microorganisms, including bacteria, actinomycete, fungi, in the root soil of A. ordosic with moss crust, was higher than that in algae-crust soil and no-crust soil in the three growth-periods of A. ordosica. On the other hand, the numbers of microorganisms in soil with BSC was higher than that in no-crust soil. These results showed that BSC can promote growth and propagation of soil microorganisms, moss crust showed more obvious effect on promoting growth and propagation of microorganisms, and the effect of algae crust was instability.3. The amount of the three types of microorganisms decreased with the increase of soil layer depth. In 0-5cm soil layer covered with A. ordosica, the amount of the three types of microorganisms in soil with moss crust was significant higher than those with algae crust. The amount of microorganisms in soil with algae crust was higher than those in no-crust soil. These results showed that soil microorganisms concentrate on the top-layer of soil, therefore, BSC has a great influence on the top-layer of soil.4. The amount of microorganisms in blooming period of A. ordosica, including bacteria, actinomycete and fungi was the highest (except individual instance), revealing the soil microorganisms have a high activity in the period. Rhizosphere effect of soil microorganisms in blooming period of A. ordosica was obvious, while BSC have no significant influence on rhizosphere effect of soil microorganisms5. The content of soil MB in fructification period was lower than that in the period for growth and blooming of A. ordosica. The content of soil microorganisms in soil covered with A. ordosica and moss crust were significant higher than that in soil covered with algae crust and no-crust soil during the three periods, and the content of soil microorganisms in soil covered with algae crust was higher than that in no-crust soil, showing that BSC can increase the content of soil MB,. The R/S of soil MB of A. ordosica was higher than 1, indicating obvious rhizosphere effect.6. Activities of Peroxidase, Urease, Proteinase and Invertase in soil covered with A. ordosica and moss crust were higher than that in soil covered with algae crust and no-crust soil (except individual instance). This result showed that biological soil crusts can enhance activity of the soil enzymes, improve the soil quality, and promote plant growth of A. ordosica.7. The R/S of Peroxidase, Polyphenol Oxidase, Urease, Proteinase and Invertase in the various soils covered with A. ordosica, were higher than one, showing obvious rhizosphere effect. Significant effect of BSC on promoting rhizosphere effect of soil enzyme of A. ordosica was not confirmed.
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