Modulations of advective gas fluxes at the soil–atmosphere interface were investigated using an enhanced experimental setup developed to perform tracer gas percolation experiments through unsaturated soil columns under well‐controlled conditions associated with long‐term and high‐resolution monitoring. The setup design includes the effect of watering and evaporation cycles, barometric pressure fluctuations, variations in the injection pressure, and plant metabolism. Although injected at a constant flux at the base of the columns, SF₆ surface fluxes varied on a timescale of hours to days. These modulations are controlled by (a) barometric pressure, (b) water content and distribution, and (c) plant metabolism. All three mainly act on the pressure gradient. Surface gas fluxes decrease under drying conditions, which increases gas porosity and the relative gas permeability and lowers the pressure gradient. Respiration of plant roots is shown to be responsible for daytime–nighttime oscillations of the tracer flux. During nighttime, O₂ consumption and CO₂ production locally lowers the pressure gradient up to the root zone due to the higher solubility of CO₂ in pore water, resulting in an increased SF₆ flux at the surface. During daytime, enhanced water loss by evapotranspiration associated with photosynthesis dominated the respiration effect and resulted in decreasing surface gas fluxes, as generally shown for drying conditions. Surface gas fluxes are therefore controlled by combined physical, chemical, and biological processes. This has important consequences, notably when discrete flux measurements are integrated in space and/or in time to quantify emissions or when used for detecting, identifying, or monitoring underground gas sources.

中文翻译：

---

非饱和土柱的高分辨率监测揭示了受生物影响的气体通量

使用增强的实验装置研究了土壤-大气界面处的对流气体通量的调制，该装置开发用于在良好控制的条件下通过长期和高分辨率监测，通过非饱和土柱进行示踪气体渗透实验。设置设计包括浇水和蒸发周期，气压波动，注入压力变化和植物新陈代谢的影响。尽管在色谱柱底部以恒定的通量注入，SF ₆表面通量在数小时至数天的时间范围内变化。这些调节受（a）气压，（b）水分含量和分布以及（c）植物代谢的控制。这三个主要作用于压力梯度。在干燥条件下，表面气体通量减少，这会增加气体孔隙率和相对气体渗透率，并降低压力梯度。植物根部的呼吸作用表现为示踪剂通量的日夜波动。在夜间，由于CO ₂在孔隙水中的溶解度较高，因此O _2的消耗和CO _2的产生会局部降低压力梯度直至根部区域，从而导致SF ₆增加表面通量。在白天，与光合作用相关的蒸散作用导致水分流失的增加主导了呼吸作用，并导致表面气体通量减少，这通常在干燥条件下表现出来。因此，通过组合的物理，化学和生物过程来控制表面气体通量。这会产生重要的后果，特别是在空间和/或时间上将离散通量测量结果集成在一起以量化排放量时，或者在将其用于检测，识别或监视地下气源时。