P25 - Multiscale Modeling
Multiscale modeling with evolving microstructure: An approach to emergence in the rhizosphere via effective soil functions
The self-organization of soil aggregates by various attracting forces influenced by geochemistry, and microbiology shall be studied by a novel, comprehensive model on the rhizosphere scale that explicitely represents the pore structure. This model should then be upscaled to the continuous root system scale.
To take into account specific properties of the rhizosphere the functional range of existing models for aggregation has to be extended and an explicit phase of mucilage as well as attachment properties of root hairs included. The project aims at the development of a mechanistic modeling approach that allows for dynamic structural reorganization of the rhizosphere at the single root scale and couples this evolving microscale model to the root system scale including the inference of soil functions. This means that we do not assume a static rhizosphere but develop a tool that is capable to dynamically track this zone on the basis of the underlying spatiotemporal aggregegate formation and geochemical patterns. To formulate the process mechanisms, a close collaboration with the experimental groups in the SPP is projected. The CT scans of the Central Experiments will reveal the pore structure with and without root hairs and thus allow inference of their influence on aggregation. We aim to model single transformation processes in the rhizosphere including mucilage and root hairs, and describe them in a rigorous way including couplings to geochemistry, microbiology, and finally to soil functions. Thus we address the following hypotheses of the SPP:
• H1: Development of self-organization in the rhizosphere in connection with spatiotemporal patterns of nutrients, water and biomass can be studied with the targeted extension of an existing model and simulation tool.
• H2: Persistence of soil structure formation will be studied as a function of the presence and development of glueing agents like mucilage and EPS.
Due to its high complexity, the rhizosphere model is not amenable to large scale computations. The homogenization techniques enable us to incorporate information from the rhizosphere scale on the macroscale. We advance upscaling techniques to dynamically evolving microstructures taking the spatiotemporal evolution of the rhizosphere into account. One major benefit of the upscaled model is that equations are coupled to hydraulic functions. The derivation of effective parameters (e.g. diffusivity, permeability) can be an important input in existing root-water uptake models taking into account the effect of mucilage and root hairs. We need a numerical approximation of the derived mechanistic model and its integration in an efficient software tool using massively parallel architecture. Such a tool is being developed to understand the formation of soil aggregates and has to be extended to include specific processes of the rhizosphere. As micro-macro problems can not be treated numerically with standard software packages, we apply numerical multiscale methods exploiting scale separation.
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