Mr. Nadav Bekin

Soil-atmosphere CO2 exchange is considered low to negligible during desiccation periods in desert soils. Recent studies challenge this paradigm, reporting a dial trend of CO2 exchange that includes nocturnal CO2 uptake and daytime efflux. Most of those studies measured soil CO2 flux using flux chambers deployed in a conventional method on a pre-inserted pipe. Those studies rarely discuss potential errors associated with using chambers in dry and bare soil conditions. We conducted an experiment using four automated chambers in Mahsash experimental farm, Central Negev, Israel, to test the effect of the pipe depth of insertion and height above the soil surface on CO2 fluxes in dry, bare soils. We found that nocturnal CO2 uptake and daytime efflux were up to 25% lower when measured on chambers deployed on pipes with an upper end elevated above the surface (the conventional method- CONV), compared to pipes with an upper part flashed with the soil surface and (DEEP). To explain this significant difference, we performed a 24-h field campaign with hourly surface temperature measurements using a thermal infrared camera. Surprisingly, CONV’s mean soil surface temperature was 2 C° higher than in DEEP throughout the day. Hence, lower soil surface temperatures increase the rate of nocturnal CO2 uptake. This may confirm our hypothesis that nocturnal CO2 uptake in desert soils is driven by dissolution of soil CO2 in adsorbed water vapors, a process expected to increase under lower temperature. The elevated pipe walls of CONV may cause a reduction in daytime advective and nocturnal radiative cooling.