Abstract: Biological soil crusts (BSCs) occur extensively in the southern part of the Gurbantunggut Desert, and serve as one of the important biological factors relating to sand surface fixation. As a winter rangeland, the desert is trampled by grazed livestock widely. Lichen crusts are the main type of BSCs in the southern part of the Gurbantonggut Desert and serve as one kind of the important nitrogen resources. They are also one of the sensitive biomonitors of desert ecosystem health, habitat heterogeneity and humaninduced disturbances. This study investigated the effect of trampling on cover of BSCs. The results were as follows: (1) The local disturbance rate mainly ranged from 10% to 20%, which was a relatively safe range against wind erosion; (2) The total coverage of BSCs was decreased due to the grazed livestock disturbance. The response of BSCs to grazing disturbance was different. Holistically, trample of grazed livestock reduced the coverage of dominant crusts, especially the lichen crusts. When disturbance rate was exceeded 30%, the average coverage of lichen crusts was lower than 30%. Because of the destroyed structure of fungalalgae symbiont, the quantity of fungi was increased (P<0.05). Contrast to the reduction of lichen crusts, more bare sand appeared with the increasing disturbance rate; (3) Grazing disturbance reduced soil organic matter content, soil bulk density and ion contents. There was an extremely significant positive correlation between soil bulk density and lichen crust coverage (P<0.01).

Key words: biological soil crust, grazing, disturbance intensity, coverage, microbial activity, Gurbantunggut Desert