| About the functions of biological soil crust (BSC) in terrestrial ecosystem in arid and semi-arid region, researchers have given full recognition. A large number of experimental studies have demonstrated that, BSC has an important function in the nutrient cycle, soil hydrological processes and soil erosion process. Based on previous studies, this paper comprehensively investigates the BSC in the special region of Mu Us Sandy Land in Northern Shaanxi, analysis physical and chemical properties of crust in different developmental levels, and lays a foundation for the further research on BSC's effect of sand-fixing in Mu Us Sandy Land. Through field plot experiments, monitoring the change of water content and study the effect of defending wind erosion in a point long term, comparing the affect of combination of vegetations and crust to water content to find a way to control Sandy desertification fundamentally. Meanwhile, we did some indoor and field cultivation experiment to explore the best temperature, soil moisture, and medium for the cultivation of bryophytes.Through experiment research, this paper gets the following results:(1) By sampling in fields in Mu Us Sandy Land in Northern Shaanxi and analysis in laboratory, physical and chemical properties and development characteristics of biological soil crust in different sampling points were mastered. This lays a foundation for the further research on soil crust's effects of windbreak and sand fixation. It was found that moss crust mainly distribute in the bottom and Leeward slope of sand and around the lake, especially below the sand vegetations. Because ground water is lower and water content is larger relatively in this region, BSC is easily to be moss crust, algal crust is only found in windward of a poplar forest. With the development of biological soil crust, its thickness growth to 11.82mm; Soil particles in biological soil crust refined, contents of particles whose diameter ranges from 0.02～0.05mm are 7.3-27.7%, higher than in sand(5.7%); Because of the refinement, bulk density of biological soil crust rises and shear strength increases apparently. PH in biological soil crust is from 7.23 to 7.81, lower than in sand; The contents of organic matter, N and K are higher in crust than in sand apparantly, but the content of P increase a little. In this research there are differences among all physical and chemical properties of biological soil crust in different sampling points. Reasons of the differences are mainly the degree of crust's development, vegetation coverage and topography and geomorphology in different sampling points.(2) Through long-term field plot on the dynamic monitoring of Soil Water, comparing water content in 6 different treatments, result indict that:pure BSC treatment can not play a positive role for water conserve in sandy land, but,as vegetation, artemisia can do this whose root system can hold water perfect. Water moisture in the treatment of combining BSC and artemisia is lower than pure artemisia treatment, higher than pure BSC treatment. However, water moisture in the treatment of combining BSC and another kind of vegetation amorpha is higher than combination of BSC and artemisia.By monitoring wind erosion in 6 treatment for 13 months, the amount of sand loss is about 788 t/hm2 in the treatment of pure sand, and the effect of wind prevention in the treatment of BSC is better than in the treatment of artemisia and amorpha. The combination of BSC and artemisia serve the effect of sand-fixing really and the mount of sand fixing reach 27.51 t/hm2, better than The combination of BSC and amorpha, whose sand loss is 55 t/hm2. Maybe it has the relation to the lower vegetation coverage.(3) Based on the nutrient analysis of moss crusts in different growing time in Mao US sandy land, modified the Knop culture medium according to the contents of N,P,K. By the method of orthogonal experimental design, did the laboratory cultivated experiment to find the optimum conditions for the growth of moss plants' tatter leaf sections. The results indicated:the best moss plants' density was 329 strains/dish, and mean height was 4.5 mm in the conditions of 15℃, low Knop as the culture medium and adding 12 ml culture medium; There was no significant difference among the treatments in the condition of 25℃and the growth was worse than in the condition of 15℃;Moss plants' tatter leaf sections did not grow in the high temperature of 35℃; According to all the plants height with the change of time, drew a growth fitting curve of moss plants:y=-0.0018x2+0.1367x. This research provided certain experimental basis on the field cultivation of moss crust, especially for the artificial recovery of biological soil crust in Mao US sandy land.4) Based on the successful laboratory cultivated experiment, the field experiment was done according to the same preparation. It contains 2 factors (shade or not, culture medium), every treatment add culture medium 1.1 L. After seven months, moss plant in the shade treatment developed well, the best is in the treatment of High Knop culture medium, the better is low Knop. Growth speed in yield is not fast, because there are some uncontrolled factors. We need do further yield cultivation research.
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