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

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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.