The diel dynamic of the CO₂ concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO₂ concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO₂ concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO₂ concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO₂ concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO₂ concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO₂ concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO₂ concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO₂ concentration. The diel oscillation of the CO₂ concentration and the hysteretic relationship between soil CO₂ concentration and air temperature were likely caused by thermal convection, leading to transport of CO₂-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO₂ concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.

与温度相关的土壤中CO ₂浓度的动态变化尚未完全了解。由于大气和土壤之间存在较大温差的地点的热对流排放，空气温度可能会控制土壤 CO ₂浓度。因此，本研究的目的是基于高频测量确定沙漠深处土壤中土壤 CO ₂浓度及其与土壤和空气温度的关系的时间动态。为此，CO ₂浓度和温度在智利北部粗质地沙漠土壤中的六个土壤深度（范围从 15 到 185 厘米）中每 60 分钟与降水和气温一起测量一年。在整个测量期间计算的平均 CO ₂浓度随土壤深度线性增加，从 15 cm 处的 463 ppm 到 185 cm 处的 1542 ppm。我们观察到 CO ₂浓度随土壤深度和表层土壤 CO ₂之间的滞后关系而降低的强烈振荡浓度以及空气和土壤温度。不同时间计算的瑞利-达西数表明土壤的热对流排放发生在夜间和清晨。一次小降水事件（4 毫米）使 15、30和 50 厘米深度的 CO ₂浓度增加了几天，但没有改变 CO ₂浓度的昼夜振荡幅度。CO ₂浓度的昼夜振荡以及土壤CO ₂浓度与气温之间的滞后关系可能是由热对流引起的，导致富含CO _{2 的}空气在夜间从土壤向大气输送。总之，我们的结果表明土壤 CO₂浓度在很大程度上可以通过温差引起的对流来控制，而不仅仅是通过扩散。这些结果具有重要意义，因为它们提供了进一步的证据，表明热对流通风有助于在大气和土壤之间经历较大温差的地点进行气体交换，这与土壤化学反应有关。