Abstract: Microflora in different soil crusts such as crust of sand dunes fixed by natural and artificial vegetation and that of flowing sand, are various. Bacteria's number is the most in all groups of microorganism, and the variation trend of the total microorganism's number rest with the amount of aerophilic bacteria. Distribution order of microbial number in different soil crusts showed that fixed sand dune with natural vegetation > sand dune with artificial vegetation of 1956 > sand dune with artificial vegetation of 1964 > semi-fixed sand dune with natural vegetation > sand dune with artificial vegetation of 1982 > sand-flowing dune without vegetation. The amount of microorganisms in soil crust of fixed sand dunes with natural vegetation was most, it is 4.46 times of sand dune with artificial vegetation in 1956, 7.44 times of sand dune with artificial vegetation in 1964, 18.52 times of semi-fixed sand dune with natural vegetation, 43.51 times of sand dune with artificial vegetation in 1982, and 90.21 times of sand-flowing dune without vegetation. Microbial number in soil crust was various with the years of sand fixed, the longer years of sand fixed, the more number of microorganism; the shorter years of sand fixed, the less number of microorganism in sand dune. Microbial number of flowing sand dunes was the least in sand dunes. Number of microbial groups in crust of artificial vegetation type are various in different seasons. It is less in summer than in autumn, the ratios of amount between in summer and in autumn was 1:4.91 in sand dune with artificial vegetation of 1956, 1:1.11 in sand dune with artificial plantation of 1964, 1:7.38 in sand dune with artificial vegetation of 1982, and 1:2.9 in sand-flowing dune without vegetation. Soil microbial number is related to ecological factors such as formation of the crust, condition of vegetation and water content of sand dunes, the longer ages of fixed sand dunes with artificial vegetation, the thicker layer of the crust, the more amount of soil microorganism, the more coverage with herbage, the less coverage with shrub. The number of soil microorganism in soil crusts are positive related to fixed degree of sand dunes.

Key words: Shapotou region, fixed sand dune, microbiotic crust, soil microflora