As an important component of ecosystem carbon (C) budgets, soil carbon dioxide (CO₂) 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 CO₂ flux (R_total), its relative importance has never been systematically assessed. In this study, after comparative measurements of CO₂ 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 CO₂ 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 CO₂, but its effect on transient CO₂ 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 CO₂ flux. Specifically, R_biotic was driven by soil temperature while R_abiotic was regulated by the change in soil temperature (ΔT). Namely, declining temperature (ΔT<0) resulted in negative R_abiotic (i.e., CO₂ went into soil) while rising temperature (ΔT>0) resulted in positive R_abiotic (i.e., CO₂ released from soil). Without recognition of R_abiotic, R_biotic would be overestimated for the daytime and underestimated for the nighttime. Although R_abiotic may not change the sum or the net value of daily soil CO₂ exchange and may not directly constitute a C sink, it can significantly alter the transient apparent soil CO₂ flux, either in magnitude or in temperature dependency. Thus, recognizing the fact that abiotic component in R_total exists widely in soils has widespread consequences for the understanding of C cycling.