The role of self-assembling of root mucilage for the formation of spatiotemporal wettability pattern in the rhizosphere

根粘液，一种多糖水凝胶，可以使土壤在干燥后疏水，缓冲根际的极端水力条件。到目前为止，人们对这种缓冲行为如何取决于粘液的化学和化学物理特性以及这些特性如何响应根际不同的环境条件知之甚少。在SPP（主题4，水通量/干旱/粘液/疏水性）的框架下，我们旨在回答以下问题：化学水凝胶性质对不同植物根粘液的物理性质起什么作用？物理性质如何影响它们的干燥行为和干燥后粘液的空间格局？在干燥和再湿润过程中，这些空间模式对根际的水力特性有哪些影响？我们的主要假设与一般SPP假设1的部分密切相关，该假设假定根际的自组织由于特定时空模式的形成而导致植物有效的水分获取。我们假设粘液是一种自组装的水凝胶，由于其特殊的化学结构，可以通过改变其超分子排列来响应周围条件的变化。超分子排列影响其物理性质，而物理性质又决定了干燥过程中多糖的空间排列，从而也决定了随后再润湿过程中的水力性质。通过不同植物黏液的透析和溶胀实验相结合，研究环境条件（pH、阳离子、表面活性物质）对水凝胶物理性质的影响，并将其与化学分析结果（单糖、连锁分析、总含量）联系起来。宏观流变学、1H-NMR（用于水的流动性）和差示扫描量热法（DSC，用于非冻结水）将与微观方法（如原子力显微镜（AFM））一起用于测定表面张力、粘度和弹性。这些AFM测量结果将作为输入参数纳入干燥过程中粘液液桥的模拟。因此，连续介质力学（描述多糖网络）的方法与晶格玻尔兹曼方法（描述孔隙空间内的水流）相结合。此外，我们将通过实验和数值量化黏液的微观干燥模式与其宏观润湿性（接触角）和宏观水力特性（如根际保水及其滞后性）之间的关系。最后，我们的结果将在小型盆栽实验（SPP玉米）中进行原位1H-NMR测量。黏液的分子化学性质和纳米尺度空间排列与宏观尺度水力过程的耦合可以显著提高我们对根际作为一个动态自组织系统的理解。

Root mucilage, a polysaccharide hydrogel, may render soil hydrophobic after drying and buffers extreme hydraulic conditions in the rhizosphere. Until now, little is known about how this buffering behavior depends on chemical and chemico-physical properties of mucilage and how these properties respond to different environmental conditions in the rhizosphere.In the frame of the SPP (topic 4, water flux/drought/mucilage/hydrophobicity), we aim at answering the following questions: Which role do chemical hydrogel properties play for the physical properties of root mucilage of different plants? How do the physical properties influence their drying behavior and the resulting spatial patterns of dried mucilage? Which consequences do these spatial patterns have for hydraulic properties of the rhizosphere during drying and rewetting?Our main hypothesis is strongly linked to the part of the general SPP hypothesis 1 that postulates that self-organization in the rhizosphere leads to an efficient water acquisition by plants due to the formation of specific spatiotemporal patterns. We hypothesize that mucilage is a self-assembled hydrogel which, due to its specific chemical structure, may respond to changes in the surrounding conditions by modifying its supramolecular arrangement. The supramolecular arrangement influences its physical properties which in turn determine the spatial arrangement of the polysaccharides during drying and by this also the hydraulic properties during the subsequent rewetting.By a combination of dialysis and swelling experiments with mucilage of different plants we will study the effect of environmental conditions (pH, cations, surface active substances) on physical hydrogel properties and link it to the results of chemical analysis (monosaccharide, linkage analysis, total contents). Macroscopic rheology, 1H-NMR (for water mobility) and differential scanning calorimetry (DSC, for non-freezing water), will be employed together with microscale methods, such as atomic force microscopy (AFM), for the determination of surface tension, viscosity and elasticity. These AFM measurements will be included as input parameters into a simulation of liquid bridges of mucilage during drying. Therefore, methods from continuum mechanics (describing the network of polysaccharids) are coupled to Lattice Boltzmann methods (describing water flow within the pore space). Furthermore, we will experimentally and numerically quantify the relation between microscopical drying patterns of mucilage to its macroscopic wettability (contact angle) and to macroscopic hydraulic properties such as rhizosphere water retention and its hysteresis. Finally, our results will be tested by insitu 1H-NMR measurements in mini pot experiments (SPP maize).Coupling molecular-chemical properties and nanoscale-spatial arrangement of mucilage with macroscale-hydraulic processes may significantly improve our understanding of the rhizosphere as a dynamic self-organized system.