Fine roots comprise plant roots with a diameter less than 2 mm and are important for plant growth and development, the soil carbon pool, and the global carbon cycle. In this research, sequential soil coring and ingrowth bag methods were used to investigate the fine root dynamics and turnover (formation, senescence, death and decomposition) of two Reaumuria soongarica communities with different physiognomy characteristics from May to October 2010 (representing the whole growing season) in the Sangong River basin. The fine root distribution, selected soil properties (such as moisture content, pH, and electrical conductivity), community structure, fine root decomposition rate, and fine root turnover of two R. soongarica communities were measured. Stepwise regression analysis was used to reveal the relationship between fine root dynamics and soil characteristics. The soil bulk density, soil water content, pH and electrical conductivity were significantly different between the two communities. The fine root biomass of the two communities showed the same trends in seasonal change and vertical distribution; for example, the fine root biomass increased gradually from May to August, and reached the maximum in August, then declined gradually from September to October. The monthly average fine root biomass of Community 1 and Community 2 was 51.55 g/m² and 133.93 g/m², respectively. The live fine-root biomass and dead fine-root biomass were 69.68% and 30.32% of total fine-root biomass in Community 1, and 72.61% and 27.39% of total fine-root biomass in the Community 2, respectively. The fine root biomass of the two communities increased initially then decreased gradually as soil depth increased. The fine root biomass was highest in the 10-20 cm soil layer, comprising 46.48% and 29.15% of the total fine root biomass in Community 1 and Community 2, respectively. The fine root decomposition rate showed a sharp decline to a minimum but thereafter increased steadily in both two communities; the annual fine root decomposition rate was 34.82% and 42.91% in Community 1 and Community 2, respectively. To reach 50% decomposition and 95% decomposition, periods of 630 days and 2933 days, respectively, for Community 1 and 467 days and 2238 days, respectively, for Community 2 were needed. Fine root net productivity of Community 1 and Community 2 was 50.67 g/m² and 178.15 g/m², respectively, and the fine root annual turnover rate in the two communities was 1.41 times/a and 1.69 times/a, respectively. The stepwise regression analysis showed that fine root dynamics were significantly influenced by soil factors such as soil moisture content, pH and electrical conductivity. Fine root growth was restricted by low soil moisture content, high soil pH, and high soil electrical conductivity, and therefore the two R. soongarica communities showed low fine root biomass and a low fine root turnover rate compared with most forest and grassland ecosystems. Nevertheless, carbon and nutrient release into the soil by fine root turnover is still an important component of the carbon and nutrient budget and is of importance for monitoring climatic change in an arid region.