As an important component of ecosystem carbon(C) budgets, soil carbon dioxide(CO_2) flux is determined by a combination of a series of biotic and abiotic processes. Although there is evidence showing that the abiotic component can be important in total soil CO_2 flux(R_(total)), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO_2 fluxes on sterilized and natural soils, the R_(total) was partitioned into biotic flux(R_(biotic)) and abiotic flux(R_(abiotic)) across a broad range of land-cover types(including eight sampling sites: cotton field, hops field, halophyte garden, alkaline land, reservoir edge, native saline desert, dune crest and interdune lowland) in Gurbantunggut Desert, Xinjiang, China. The relative contribution of R_(abiotic) to R_(total), as well as the temperature dependency and predominant factors for R_(total), R_(biotic) and R_(abiotic), were analyzed. Results showed that R_(abiotic) always contributed to R_(total) for all of the eight sampling sites, but the degree or magnitude of contribution varied greatly. Specifically, the ratio of R_(abiotic) to R_(total) was very low in cotton field and hops field and very high in alkaline land and dune crest. Statistically, the ratio of R_(abiotic) to R_(total) logarithmically increased with decreasing R_(biotic), suggesting that R_(abiotic) strongly affected R_(total) when R_(biotic) was low. This pattern confirms that soil CO_2 flux is predominated by biotic processes in most soils, but abiotic processes can also be dominant when biotic processes are weak. On a diurnal basis, R_(abiotic) cannot result in net gain or net loss of CO_2, but its effect on transient CO_2 flux was significant. Temperature dependency of R_(total) varied among the eight sampling sites and was determined by the predominant processes(abiotic or biotic) of CO_2 flux. Specifically, R_(biotic) was driven by soil temperature while R_(abiotic) was regulated by the change in soil temperature(ΔT). Namely, declining tempe
