Rethinking the deployment of static chambers for CO₂ flux measurement in dry desert soils

Abstract. The mechanisms underlying the soil CO₂ flux (Fs) in dry desert soils are not fully understood. To better understand these processes, we must accurately estimate these small fluxes. The most commonly used method, static chambers, inherently alter the conditions that affect the flux and may introduce errors of the same order of magnitude as the flux itself. Regional and global assessments of annual soil respiration rates are based on extrapolating point measurements conducted with flux chambers. Yet, studies conducted in desert ecosystems rarely discuss potential errors associated with using static chambers in dry and bare soils. We hypothesized that a main source of error is the collar protrusion above the soil surface. During the 2021 dry season, we deployed four automated chambers on collars with different configurations in the Negev Desert, Israel. Fs exhibited a repetitive diel cycle of nocturnal uptake and daytime efflux. CO₂ uptake measured over the conventionally protruding collars was significantly lower than over the collars flushed with the soil surface. Using thermal imaging, we proved that the protruding collar walls distorted the ambient heating and cooling regime of the topsoil layer, increasing the mean surface temperatures. Higher soil temperatures during the night suppressed the flux driving forces, i.e., soil-atmosphere CO₂ and temperature gradients, ultimately leading to an underestimation of up to 50 % of the actual Fs. Accordingly, the total daily CO₂ uptake by the soil in the conventionally deployed collars was underestimated by 35 %. This suggests that desert soils are a larger carbon sink than previously reported and that drylands, which cover approximately 40 % of Earth’s terrestrial surface, may play a significant role in the global carbon balance.