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We evaluated the influence of exposure to ultraviolet-B (UV-B) radiation (2.75, 3.08, 3.25 and 3.41 W m(-2)), and recovery on returning to visible light conditions (150 mu mol m(-2) S-1) on the physiological properties related to photosynthesis in the mosses Bryum argenteum Hedw. and Didymodon vinealis (Brid.) Zand. Specimens of B. argenteum and D. vinealis were isolated from biological soil crusts (BSCs) from the Tengger Desert, northern China. The results showed that UV-B radiation decreased the CM fluorescence parameters, photosynthetic pigments, soluble protein and malondialdehyde (MDA) contents of B. argenteum and D. vinealis, and that the degree of negative effects was in proportion to the intensity of UV-B radiation. The CM fluorescence parameters, photosynthetic pigments, soluble protein and MDA contents of B. argenteum and D. vinealis increased when they were returned to visible light after UV-B radiation. There were gradual decreases in recovery ability with increasing UV-B intensity. Experiments conducted to determine the ability of BSCs to recover from UV-B stress when exposed at different intensities show they have some capacity to recover from the stress. Enhanced UV-B radiation causes changes in the composition and structure of BSCs that could impair their protective ecological functions in desert areas.