AimsRhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and mucilages on hydraulic properties of soils depends on their physicochemical characteristics and origin.MethodsSurface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and mucilages at 0.46 and 4.6 mg g−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential.ResultsSurface tension decreased and viscosity increased with increasing concentration of the exudates and mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and mucilages on soil water retention almost ceased when approaching wilting point at −1500 kPa matric potential.ConclusionsBarley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.

中文翻译：

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根际沉积物和种子粘液的表面张力、流变性和疏水性影响土壤保水性和滞后性

目的将从玉米和大麦根部的水培溶液中收集的根沉积物以及从奇亚籽中洗涤的种子粘液添加到土壤中，以测量它们在一定浓度范围内对沙壤土中保水性和滞后性的影响。我们检验了植物分泌物和粘液对土壤水力性质的影响取决于其物理化学特性和来源的假设。方法分别使用杜努伊环法和锥板流变仪测量分泌物溶液的表面张力和粘度。采用座滴法测量水在渗出液处理过的土壤上的接触角。通过在充满已知渗透势的聚乙二醇 (PEG) 溶液的透析管上平衡土壤样品（用浓度为 0.46 和 4.6 mg g−1 的渗出液和粘液处理）来测量保水性和滞后性。结果随着渗透压的增加，表面张力降低，粘度增加溶液中渗出物和粘液的浓度。奇亚籽渗出物的表面张力和粘度变化最大，而大麦根渗出物的表面张力和粘度变化最小。接触角随着土壤中玉米根和奇亚籽分泌物浓度的增加而增加，但大麦根则不然。奇亚籽粘液和玉米根根沉积物增强了土壤保水性并增加了滞后指数，而大麦根根沉积物降低了土壤保水性和滞后效应。当接近-1500 kPa基质势的萎蔫点时，渗出物和粘液对土壤保水的影响几乎停止。结论大麦根际沉积物表现为表面活性剂，在较小的吸力下干燥根际。奇亚籽粘液和玉米根根沉积物表现为水凝胶，在根际保留更多水分，但再润湿速度较慢，滞后作用较大。