An inter-seasonal analysis of abiotic factors involved in the surface and subsurface fluxes of CO2 in desert soils

The soil CO2 efflux is the largest terrestrial source of CO2 to the atmosphere, primarily driven by the metabolic activity of soil organisms. Consequently, it has often been considered low to negligible in desert soils. However, the contribution of abiotic factors to the soil CO₂ flux could be significant in desert soil, particularly during dry periods when observed diel patterns of CO₂ exchange appear to contradict conventional expectations. I will show evidence that atmospheric water vapor, adsorbed to soil particles at night, supplies the water to dissolve gaseous CO₂. This process reduces CO₂ concentrations in the soil pore space and can explain the diel pattern of CO₂ exchange reported in dry periods. To show this, I used various field and laboratory methods during two field experiments in the Sahara Desert, Morocco, and the Negev Desert, Israel. Finally, I will discuss the relative contribution of dry and wet periods to the total yearly carbon balance and show how summer heat waves, which increase the daily minimum air temperature, may intensify carbon losses from the soil.