Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils
Nonequilibrium water dynamics in the rhizosphere: How mucilage affects water flow in soils
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DOI：
10.1002/2013wr014756
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发表时间：
2014-08-01
影响因子：
5.4
通讯作者：
Carminati, Andrea
中科院分区：
文献类型：
--
作者：
Kroener, Eva;Zarebanadkouki, Mohsen;Carminati, Andrea
从土壤到植物根部的水流受到靠近根部的狭窄土壤区域（即根际）的特性控制。特别是，根际的水力特性被粘液（根部分泌的聚合物凝胶）改变。在本文中，我们提出了混合粘液的非饱和土壤中水流的实验结果和概念模型。该模型的一个中心假设是，与大块土壤相比，粘液的干/湿率不同，导致根际含水量和水势之间的非平衡关系。我们将这种非平衡关系与理查兹方程耦合起来，得到了土壤和粘液中水流的本构方程。为了测试模型假设，我们测量了与奇亚籽粘液混合的沙土的保水曲线和饱和导水率。此外，我们使用中子射线照相术对干燥和湿润循环期间与粘液混合的土壤层中的水含量进行成像。射线照片显示土壤-粘液混合物中存在非平衡水动力学。通过数值求解非平衡模型来模拟实验。我们的研究提供了概念和实验证据，表明粘液对土壤水动态有很大影响。在干燥过程中，粘液可以长时间保持较高的土壤含水量，而在灌溉过程中，粘液可以延迟土壤的再湿润。我们假设根部的粘液分泌通过调节根际水分含量动态来减轻植物水分胁迫。
The flow of water from soil to plant roots is controlled by the properties of the narrow region of soil close to the roots, the rhizosphere. In particular, the hydraulic properties of the rhizosphere are altered by mucilage, a polymeric gel exuded by the roots. In this paper we present experimental results and a conceptual model of water flow in unsaturated soils mixed with mucilage. A central hypothesis of the model is that the different drying/wetting rate of mucilage compared to the bulk soil results in nonequilibrium relations between water content and water potential in the rhizosphere. We coupled this nonequilibrium relation with the Richards equation and obtained a constitutive equation for water flow in soil and mucilage. To test the model assumptions, we measured the water retention curve and the saturated hydraulic conductivity of sandy soil mixed with mucilage from chia seeds. Additionally, we used neutron radiography to image water content in a layer of soil mixed with mucilage during drying and wetting cycles. The radiographs demonstrated the occurrence of nonequilibrium water dynamics in the soil-mucilage mixture. The experiments were simulated by numerically solving the nonequilibrium model. Our study provides conceptual and experimental evidences that mucilage has a strong impact on soil water dynamics. During drying, mucilage maintains a greater soil water content for an extended time, while during irrigation it delays the soil rewetting. We postulate that mucilage exudation by roots attenuates plant water stress by modulating water content dynamics in the rhizosphere.