On the apparent CO₂ absorption by alkaline soils

Abstract. Alkaline soils in the Gubantonggut Desert were recently demonstrated socking away large quantities of CO₂ in an abiotic form. This demands a better understanding of abiotic CO₂ exchange in alkaline sites. Reaction of CO₂ with the moisture or dew in the soil was conjectured as a potential mechanism. The main goal of this study is to determine the extent to which the dew deposition modulates Land–Atmosphere CO₂ exchange at highly alkaline sites (pH ~ 10). Experiments were conducted at the most barren sites (canopy coverage < 5%) to cut down uncertainty. Dew quantities and soil CO₂ fluxes were measured using a micro-lysimeters and an automated flux system (LI-COR, Lincoln, Nebraska, USA), respectively. There is an evident increase of dew deposition in nocturnal colder temperatures and decrease in diurnal warmer temperatures. Variations of soil CO₂ flux are almost contrary, but the increase in diurnal warmer temperatures is obscure. It was shown that the accumulation and evaporation of dew in the soil motivates the apparent absorption and release of CO₂. It was demonstrated that dew amounts in the soil has an exponential relation with the part in F_c beyond explanations of the worldwide utilized Q₁₀ model. Therefore dew deposition in highly alkaline soils exerted a potential CO₂ sink and can partly explain the apparent CO₂ absorption. This implied a crucial component in the net ecosystem carbon balance (NECB) at alkaline sites which occupies approximately 5% of the Earth's land surface (7 million km). Further explorations for its mechanisms and representativeness over other arid climate systems have comprehensive perspectives in the quaternary research.