Abiotic CO₂ exchange between soil and atmosphere and its response to temperature

Although abiotic CO₂ exchange between soil and atmosphere is often observed in deserts, its contribution to carbon balance and accurate response to soil temperature (T _s (°C)) are still uncertain. Abiotic soil carbon flux (ASCF) and T _s were continuously measured on sterilized soil at 2-day intervals in the Mu Us Desert, northwestern China from May to October in 2012. The results showed that negative ASCF (CO₂ absorption) occurred at night while positive ASCF (CO₂ emission) during the day. Net CO₂ sequestration during the 6 months totaled 64.37 g CO2 m⁻² (0.09 μmol m⁻² s⁻¹). On the seasonal scale, ASCF was weakly correlated with T _s (γ = 0.15, p < 0.01), but showed a strong positive correlation with the rate of change in T _s (ΔT/Δt (°C h⁻¹)) (γ = 0.82, p < 0.01). On the diurnal scale, ASCF showed clear hysteresis loops with respect to T _s , but ΔT/Δt explained more than 85 % of the diurnal variations in ASCF for different months. The results indicate that a non-trivial CO₂ exchange process between soil and atmosphere can induce carbon sequestration and this exchange process is modified by temperature. Although soil temperature cannot be directly used to explain the effect of temperature on the abiotic soil carbon flux, the rate of change in soil temperature can accurately interpret the role of temperature played in the abiotic CO₂ exchange between soil and atmosphere. CO₂ absorption and emission by the desert soil is driven by the rate of falling and rising of T _s, respectively. The findings may have significant implications for the global carbon cycle and may facilitate to explore the formation of this abiotic CO₂ exchange process.