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Winter soil respiration (R-s) is becoming a significant component of annual carbon budgets with more warming in winter than summer. However, little is known about the controlling mechanisms of winter R-s in dryland. We made continuous measurements of R-s in four microsites (non-crust (BS), lichen (LC), moss (MC), and a mixture of moss and lichen (ML)) in a desert shrub-land ecosystem northern China, to investigate the causes of R-s dynamics in winter. The mean winter R-s ranged from 0.10 to 0.17 mu mol CO2 m(-2).s(-1) across microsites, with the highest value in BS. Winter Q(10) (known as the increase in respiration rate per 10 degrees C increase in temperature) values (2.8-19) were much higher than those from the growing season (1.5). R-s and Q(10) were greatly enhanced in freeze-thaw cycles compared to frozen days. Diurnal patterns of R-s between freeze-thaw and frozen days differed. Although the freeze-thaw period was relatively short, its cumulative R-s contributed significantly to winter R-s. The presence of biocrust might induce lower temperature, thus having fewer freeze-thaw cycles relative to bare soil, leading to the lower R-s for microsites with biocrusts. In conclusion, winter R-s in drylands was sensitive to soil temperature (T-s) and T-s-induced freeze-thaw cycles. The temperature impact on R-s varied among soil cover types. Winter R-s in drylands may become more important as the climate is continuously getting warmer.