Studies on soil carbon flux in biologically crusted soil in Gurbantunggut desert have shown temperature sensitivity of soil carbon flux differed between crust types, and moreover, significant difference of soil carbon flux between crust types was dependent on precipitation size. These results suggest that physiological activities and soil organic carbon stability in crusted soil may be related with the development of biological soil crusts, and are responsible for variation in soil carbon flux. In this project, firstly, we will investigate soil carbon stability and its dependence on regional precipitation, temperature and soil texture, as well as biotic parameters of biological crusts in typical crusted soil of five chosen sites in northern China, and expect to elucidate the variability of soil carbon stability and its potential direct and indirect relations with the above parameters. Secondly, we will examine the soil organic carbon decomposition responses of a group of four soil particle sizes to a gradient of soil moistures and temperatures, and expect to know the dependence of soil organic carbon stability related with soil particle size on soil moisture and temperature in biologically crusted soil. At last, specifically taking biologically crusted soil in Gurbantunggut desert as an example, we will measure soil organic carbon decomposition after simulated precipitation in field and after additions of microbial selective inhibitors, glucose, starch, NH4NO3 in lab, and expect to elucidate effects of microbial functional type and microbial organic carbon utilization type in crust organisms on soil organic carbon stability. Through the above studies, we will elucidate the effects of biological soil crusts on soil organic carbon stability in arid and semiarid regions.