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Different from soils in other ecosystems, soils in arid and semiarid areas are covered by biological soil crusts, which can both assimilate and release carbon via their physiological activities. Nevertheless, few studies have evaluated carbon flux in biologically crusted soils. In the current study, we investigated the daily carbon flux in moss- and cyanobacterial/lichen-crusted soils, as well as crust-removed soil (referred as bareland) in the Gurbantunggut Desert, Northwestern China from April to October 2010. We also investigated carbon flux in biologically crusted soils after 0, 2, 5, and 15 mm precipitation treatments. Carbon flux between crusted soil and bareland had no significant difference, with average values of 0.16, 0.2, and 0.12 mu mol m(-2) S-1 for moss-crusted soil, cyanobacterial/lichen crusted soil, and bareland. respectively. The corresponding (210 values for the three soils were 2.9, 3.5, and 1.9, respectively. Precipitation significantly elicited carbon flux, reaching a maximum value of 2.4 mu mol m(-2) s(-1). After precipitation, the net carbon flux in light was lower than that in dark respiration. No carbon influx was observed in light condition. The average carbon flux rate and total carbon production increased exponentially with the precipitation amount. This study indicates that biological soil crusts do not increase the respiration of soil, but increases the temperature dependence of soil carbon flux because of the higher microbial biomass than bareland. (C) 2012 Elsevier B.V. All rights reserved.