Speaker
Description
Plant productivity is directly influenced by water and nutrient uptake. Therefore, functional-structural root models need to accurately describe rhizosphere processes. Such models will enable better agricultural management strategies and improved root trait selection for plant breeding. Due to their complexity functional-structural root models are hard to analyse. In Schnepf et al. (2020) various research groups developed a systematic framework for benchmarking individual root functional models and their individual components. In this work we will focus on root water uptake and how appropriate sink terms can be developed in macroscopic (plot-scale) models.
Macroscopic water movement is commonly described by the Richards equation and the impact of root water uptake is described by a sink term. The sink term is either derived by some averaging or homogenisation procedure or by equations based on empirical observations. Common choices are to set the sink term proportional to the root surface density, or to use line sources which represent the root architecture. In Schnepf et al. (2020) various sink terms were benchmarked and compared to an exact 3-dimensional solution of a small root system, where a mesh was calculated and refined towards the root surface. Results showed that local water depletion in the rhizosphere will affect total water uptake when the soil is sufficiently dry.
A solution to this problem was presented by Mai et al. (2019) who described the rhizosphere by a 1-dimensional model around each root segment. The 1-dimensional grid was refined at the root surface enabling an accurate representation of the pant-soil interface. In the following we describe and generalize the coupling steps, especially with a focus on the point of contacts between the different sub models (see Figure 1). The evolving root architecture is described by CPlantBox (Schnepf et al, 2018), macroscopic water movement as well as water movement in the 1D rhizosphere models are calculated in DuMux (Flemisch et al. 2011, Koch et al. 2020).
Using 1d-cylindrical models to describe the plant rhizosphere is a promising approach for development of better functional-structural root models. It enables us to separately develop and analyse the microscopic rhizosphere models. Such models can be directly used in the proposed coupling framework, where no additional upscaling is needed. This enables an analysis how changes of microscopic parameters will affect the macroscopic results.
References
A. Schnepf, C. K. Black, V. Couvreur, B. M. Delory, C. Doussan, A. Koch, … & M. Weber (2020) Call for participation: Collaborative benchmarking of functional-structural root architecture models. The case of root water uptake, Frontiers in plant science 11.
TH. Mai, A. Schnepf, H. Vereecken, J. Vanderborght (2019) Continuum multiscale model of root water and nutrient uptake from soil with explicit consideration of the 3D root architecture and the rhizosphere gradients. Plant and Soil 439 (1), 273-292.
A. Schnepf, D. Leitner, M. Landl, G. Lobet, T. H. Mai, S. Morandage, C. Sheng, M. Zörner, J. Vanderborght, H. Vereecken (2018) CRootBox: a structural–functional modelling framework for root systems. Annals of botany 121 (5), 1033-1053
T. Koch, D. Gläser, K. Weishaupt, S. Ackermann, M. Beck, B. Becker, ... & B. Flemisch(2021). DuMux 3–an open-source simulator for solving flow and transport problems in porous media with a focus on model coupling. Computers & Mathematics with Applications, 81, 423-443.
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