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The changes in climate can result in several environmental stress factors. Among these, ultraviolet- B (UV-B) and water-deficit have serious detrimental effects on plants at the physiological, morphological, and biochemical levels. Biological soil crusts (BSCs), formed by an association between soil particles and photosynthetic algae, cyanobacteria, lichens, and mosses in varying proportions, are a key functional feature of arid and semi-arid areas. In this study, Bryum argenteum, isolated from BSCs found in the Tengger Desert, China, was subjected to UV-B and water-deficit, singly and in combination, in a greenhouse for 10 days. The treatments consisted of four UV-B levels (2.75, 3.08, 3.25, and 3.41 W/m(2)) and two water application levels (well-watered and water-deficit). UV-B treatment and water-deficit singly caused a significant decrease in chlorophyll (Chl) fluorescence parameters, carotenoid (Car), total flavonoid contents, and a significant increase in MDA content. The combined application of UV-B and water-deficit produced significantly higher Chl fluorescence parameters, Chl, Car and total flavonoid contents, but reduced MDA content. These results suggest that water-deficit alleviates the negative effects on B. argenteum caused by enhanced UV-B radiation. Our results provide novel insights into understanding the relationships between BSCs and environmental factors, and supply a theoretical foundation for BSC assessment and protection in arid and semi-arid regions.