Combined quantitative three-dimensional imaging and predictive modeling of soil water movement and root water uptake

植物从土壤中提取水分和养分的能力取决于根系附近土壤（根际）的运输特性。反之亦然，根际的结构和水力受到根和相关微生物的强烈影响。改善根-土相互作用是优化作物生产的一个重要方面，但需要更好地了解根际结构和生化变化如何影响水分和养分流入根系。非侵入性成像技术提供了进入根际的实验途径，而建模技术的进步使根区运输过程的三维计算成为可能。两者的结合今天被认为是最有希望的方式，以提高对根和土壤的复杂和动态相互作用的理解。该项目的目标是获取根构型、动态土壤水分分布和根际土壤微观结构的互补三维成像信息，并将这些信息整合到三维水运模型中，以全面描述和预测根际的水通量，包括相关的根吸收。我们将应用一种新型的超快中子层析成像技术来研究土壤中的水分运动和时间分辨三维（迄今为止只能在二维）的根部转移。进一步的由根引起的土壤水力学变化将在靠近根的地方进行研究，因为根渗出物和压实的影响是最大的。通过应用空间分辨率大大提高的专用中子装置，我们将能够以前所未有的精度分析根-土界面的三维水梯度，以评估不同类型土壤的粘液渗出对土壤水力学的潜在影响。最后，中子和x射线层析成像实验将结合起来，同时获得根系结构、水分分布和土壤微观结构的补充信息。这些实验的目的是将根际的具体水力行为与在该土壤区域观察到的微观结构不均匀性联系起来。成像方法的总体目标是提供土壤中三维水流的全面图像，以及随后通过根系的水流。我们将直接将成像结果集成到数值流动和运输模拟器DuMux中，以增强和使用其对水流和根系吸收的预测能力，以实现现实的3D根系体系结构。总而言之，我们希望将完整的土壤生长根系的时间分辨三维信息转化为根系内部水流、根系水分吸收和水分转移的一对一瞬态三维模拟。这是一个必要的和期待已久的步骤，以解决由根际的动态和三维性质所带来的巨大挑战，根际被认为是理解从土壤到植物的水转移的关键界面。

The ability of plants to extract water and nutrients from soil depends on the transport properties of the soil next to the roots, the rhizosphere. Vice versa, structure and hydraulics of the rhizosphere are strongly impacted by roots and associated microbes. Improvement of root-soil interaction is a crucial aspect for optimizing crop production, yet, requires better understanding of how structural and biochemical changes of the rhizosphere affect water and nutrient fluxes into roots. Non-invasive imaging techniques provide experimental access to the rhizosphere while advances in modeling allow for three-dimensional calculations of transport processes in the root zone. The combination of both is considered today the most promising way to improve the understanding of the complex and dynamic interplay of roots and soil. The goal of this project is to capture complementary 3D imaging information on root architecture, dynamic soil water distribution and microstructure of rhizosphere soil and to integrate this information into a 3D water transport model to comprehensively describe and predict water fluxes through the rhizosphere including the related root uptake. We will apply a novel ultra-fast neutron tomography technique to study water movement in the soil and transfer into the roots time-resolved in three dimensions (which was so far possible in 2D only). Further root induced modifications of the soil hydraulics will be studied in close proximity to roots, where the impact of root exudates and compaction is highest. By applying a dedicated neutron set-up with greatly enhanced spatial resolution we will be able to analyze 3D water gradients at the root-soil interface in unprecedented accuracy to evaluate the potential influence of mucilage exudation on the soil hydraulics for distinct types of soil. Finally neutron and X-ray tomography experiments will be combined to simultaneously access complementary information on the root system architecture, water distribution and soil microstructure. The aim of these experiments is to link the specific hydraulic behavior of the rhizosphere with microstructural inhomogeneities observed in this soil region. The overall objective of the imaging approach is to provide a comprehensive picture of the 3D water flow in soil, but also subsequently through the root system. We will directly integrate the imaging results into the numerical flow and transport simulator DuMux to enhance and use its predictive power for water flow and root uptake for realistic 3D root system architectures. In sum, we want to transfer time-resolved 3D information of a complete, soil-grown root-system into a one-to-one, transient 3D simulation of water flow, root water uptake and water transfer inside the root system. This is a necessary and long-awaited step to tackle the great challenges given by the dynamic and three-dimensional nature of the rhizosphere, which is considered the key interface to understand water transfer from soil to plant.