Abstract: Taking Bryum argenteum and Didymodon vinealis crusts from an artificial vegetation area of south-eastern fringe of the Tengger Desert in northwestern China（37°32′-37°26′N， 105°02′-104°30′E）as a test object，to determine the influence of enhanced UV-B radiation on the osmotic adjustment of substances， membrane integrity， and the antioxidant enzyme system in laboratory. Simulating the depletion of the stratospheric ozone layer by 0%（control） ， 6%， 9%， and 12% to obtain the levels of UV-B（2.75， 3.08， 3.25， and 3.41 W · m ^-2 ） ， respectively. The results showed that the malondialdehyde（MDA）content of B. argenteum and D. vinealis significantly increased，while the soluble sugar content， SOD， and CAT activities decreased， with increased UV-B intensity. Moreover， the effects of soluble sugar content， MDA content， SOD， and CAT activities after UV-B exposure were greater in B. argenteum than that in D. vinealis， and suggested that B. argenteum was more sensitive to enhanced UV-B radiation than D. vinealis. These results also indicate that the composition and structure of biological soil crusts（BSC）will significantly change under future enhanced UV-B radiation， and these changes will profoundly influence the functioning of BSC in deserts and influence the health and stability of these ecosystems.

Key words: ultraviolet-B（UV-B）, biological soil crust, osmotic adjustment, malondialdehyde（MDA）, antioxidant enzyme