Pore-Scale Distribution of Mucilage Affecting Water Repellency in the Rhizosphere
Pore-Scale Distribution of Mucilage Affecting Water Repellency in the Rhizosphere
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DOI：
10.2136/vzj2017.01.0013
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发表时间：
2018-02-01
影响因子：
2.8
通讯作者：
Carminati, A.
中科院分区：
文献类型：
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作者：
Benard, P.;Zarebanadkouki, M.;Carminati, A.
根际土壤的物理性质受根分泌物粘液的强烈影响，越来越多的证据表明粘液对土壤干燥时的润湿性有影响。我们介绍了土壤干燥过程中粘液沉积的概念模型及其对土壤润湿性的影响。我们假设，随着土壤的干燥，水的半月面会后退，并将粘液吸引到颗粒之间的接触区。在粘液含量较低时(每克土壤含毫克)，粘液沉积物呈细丝状，可被渗入的水绕过。在较高含量时，粘液沉积占据了很大一部分孔隙空间，使根际疏水。显微镜图像和接触角测量证实了这一假设。我们测量了石英砂(直径为0.125-0.63 mm和0.125-0.2 mm)、粉砂(直径为36-63 mm)和玻璃微珠(直径为0.1-0.2 mm)与不同剂量的CHIA(Salvia hispanica L.)种子粘液(干含量范围为0.2-19 mg g(-1))。我们观察到了一种类似于阈值的拒水性发生。在粘液含量较低的情况下，水滴在300ms内渗入。当超过临界粘液含量时，土壤颗粒-粘液混合物就变成了防水性。土壤临界粘液含量随土壤颗粒大小的增加而降低。在这一临界含量以上，粘液沉积具有中空圆柱体的形状，占据了很大一部分孔隙空间。在临界粘液含量以下，粘液沉积呈细丝状。这项研究展示了粘液分布的微观非均质性如何影响粘液包裹的土壤颗粒的宏观润湿性。
The physical properties of the rhizosphere are strongly influenced by root-exuded mucilage, and there is increasing evidence that mucilage affects the wettability of soils on drying. We introduce a conceptual model of mucilage deposition during soil drying and its impact on soil wettability. We hypothesized that as soil dries, water menisci recede and draw mucilage toward the contact region between particles. At low mucilage contents (milligrams per gram of soil), mucilage deposits have the shape of thin filaments that are bypassed by infiltrating water. At higher contents, mucilage deposits occupy a large fraction of the pore space and make the rhizosphere hydrophobic. This hypothesis was confirmed by microscope images and contact angle measurements. We measured the initial contact angle of quartz sand (0.5-0.63- and 0.125-0.2-mm diameter), silt (36-63-mm diameter), and glass beads (0.1-0.2-mm diameter) mixed with varying amounts of chia (Salvia hispanica L.) seed mucilage (dry content range 0.2-19 mg g(-1)) using the sessile drop method. We observed a threshold-like occurrence of water repellency. At low mucilage contents, the water drop infiltrated within 300 ms. Above a critical mucilage content, the soil particle-mucilage mixture turned water repellent. The critical mucilage content decreased with increasing soil particle size. Above this critical content, mucilage deposits have the shape of hollow cylinders that occupy a large fraction of the pore space. Below the critical mucilage content, mucilage deposits have the shape of thin filaments. This study shows how the microscopic heterogeneity of mucilage distribution impacts the macroscopic wettability of mucilage-embedded soil particles.