Abstract: As the important component of the ecosystem respiration，knowledge of soil CO₂ flux is essential for understanding the global carbon dynamics under future climate scenarios. But studies on soil CO₂ flux in saline desert ecosystems are scarce compared to their broad distribution. Therefore， based on the in situ measurement of soil CO₂ flux，the paper analyzed the diurnal and seasonal variation of soil CO₂ flux at a saline desert. Particularly aiming to the negative flux（CO₂ enters rather than releasing from the ground），autoclaving treatment was used to partitioning soil total CO2 flux into biotic and abiotic component at four different saline/alkaline soils. The results show that soil CO₂ flux under the canopy are significantly higher than that in inter-plant spaces （P<0.05）. The soil CO2 flux，neither under the canopy nor in inter-plant spaces，exhibited any obvious seasonal variations because of the bi-modal diurnal patterns，which were probably caused by the inhibition of microbial activity by extremely high temperature. Specially，soil CO₂ flux in inter-plant spaces exhibited negative flux，which means CO₂ enters rather than releasing from the soil surface，the reason of which was the abiotic processes. When soil water content equals 10%，the contribution of abiotic flux to soil total CO₂ flux ranged from 18.6% to 49.2%，with a linearly increasing trend with increasing pH，by contrast，soil abiotic component is predominant in air-dried soil. Thus，soil pH and soil water content has great effect on soil abiotic flux，which must be a substantial component of soil CO₂ flux in saline/alkaline soils.

Key words: soil CO₂ flux, biotic process （flux）, abiotic process （flux）, pH, soil water content