Root System Scale Models Significantly Overestimate Root Water Uptake at Drying Soil Conditions

Khare, Deepanshu; Vereecken, Harry; Schnepf, Andrea; Leitner, Daniel; Vanderborght, Jan; Selzner, Tobias

doi:10.3389/fpls.2022.798741

Journal Article

FZJ-2022-02590

Root System Scale Models Significantly Overestimate Root Water Uptake at Drying Soil Conditions

Khare, D. (Corresponding author)FZJ* ; Selzner, T. (Corresponding author)FZJ* ; Leitner, D.FZJ* ; Vanderborght, J.FZJ* ; Vereecken, H.FZJ* ; Schnepf, A.FZJ*

2022
Frontiers Media Lausanne

Frontiers in Functional Plant Ecology 13, 798741 (2022) [10.3389/fpls.2022.798741]

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Please use a persistent id in citations: http://hdl.handle.net/2128/31454 doi:10.3389/fpls.2022.798741

Abstract: Soil hydraulic conductivity (ksoil) drops significantly in dry soils, resulting in steep soil water potential gradients (ψs) near plant roots during water uptake. Coarse soil grid resolutions in root system scale (RSS) models of root water uptake (RWU) generally do not spatially resolve this gradient in drying soils which can lead to a large overestimation of RWU. To quantify this, we consider a benchmark scenario of RWU from drying soil for which a numerical reference solution is available. We analyze this problem using a finite volume scheme and investigate the impact of grid size on the RSS model results. At dry conditions, the cumulative RWU was overestimated by up to 300% for the coarsest soil grid of 4.0 cm and by 30% for the finest soil grid of 0.2 cm, while the computational demand increased from 19 s to 21 h. As an accurate and computationally efficient alternative to the RSS model, we implemented a continuum multi-scale model where we keep a coarse grid resolution for the bulk soil, but in addition, we solve a 1-dimensional radially symmetric soil model at rhizosphere scale around individual root segments. The models at the two scales are coupled in a mass-conservative way. The multi-scale model compares best to the reference solution (−20%) at much lower computational costs of 4min. Our results demonstrate the need to shift to improved RWU models when simulating dry soil conditions and highlight that results for dry conditions obtained with RSS models of RWU should be interpreted with caution.

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