Gas exchange in the soil is determined by the size and connectivity of air‐filled pores. Root mucilage reduces air‐filled pore connectivity and thus gas diffusivity. It is unclear to what extent mucilage affects soil pore connectivity and tortuosity. The aim of this study was to gain a better understanding of gas diffusion processes in the rhizosphere by explaining the geometric alterations of the soil pore space induced by mucilage. We quantified the effect of a root mucilage analogue collected from chia seeds without intrinsic respiratory activity on oxygen diffusion at different water contents during drying–rewetting cycles in a diffusion chamber experiment. Quantification of oxygen diffusion showed that mucilage decreased the gas diffusion coefficient in dry soil without affecting air‐filled porosity. Without mucilage, a hysteresis in gas diffusion coefficient during a drying–rewetting cycle was observed. The effect depended on particle size and diminished with increasing mucilage content. X‐ray computed tomography imaging indicated a hysteresis in the connectivity of the gas phase during a drying–rewetting cycle for samples without mucilage. This effect was attenuated with increasing mucilage content. Furthermore, electron microscopy showed that mucilage structures formed in drying soil increase with mucilage content, thereby progressively reducing the connectivity of the gas phase. In conclusion, the effect of mucilage on soil gas diffusion highly depends on soil texture and mucilage content. The diminishing hysteresis with the addition of mucilage suggests that plant roots secrete mucilage to balance oxygen availability and water content, even under fluctuating moisture conditions.

中文翻译：

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奇亚籽的根粘液类似物可降低土壤气体扩散率


土壤中的气体交换取决于充满空气的孔隙的大小和连通性。根粘液降低了充满空气的孔隙连通性，从而降低了气体扩散率。目前还不清楚粘液在多大程度上影响土壤孔隙的连通性和弯曲度。本研究的目的是通过解释粘液引起的土壤孔隙空间的几何变化，更好地了解根际气体扩散过程。我们量化了从奇亚籽中收集的不具有内在呼吸活性的根粘液类似物在扩散室实验中的干燥-再润湿循环期间在不同含水量下对氧气扩散的影响。氧扩散的量化表明，粘液降低了干燥土壤中的气体扩散系数，而不影响充气孔隙率。在没有粘液的情况下，在干燥-再润湿循环期间观察到气体扩散系数的滞后。该效果取决于颗粒大小，并随着粘液含量的增加而减弱。 X 射线计算机断层扫描成像表明，对于不含粘液的样品，在干燥-再润湿循环期间，气相的连通性存在滞后现象。这种效应随着粘液含量的增加而减弱。此外，电子显微镜显示，干燥土壤中形成的粘液结构随着粘液含量的增加而增加，从而逐渐降低气相的连通性。总之，粘液对土壤气体扩散的影响很大程度上取决于土壤质地和粘液含量。随着粘液的添加而减少的滞后表明，即使在水分波动的条件下，植物根也会分泌粘液来平衡氧气可用性和水含量。