Call for Participation: Collaborative Benchmarking of Functional-Structural Root Architecture Models. The Case of Root Water Uptake

Abstract

Three-dimensional models of root growth, architecture and function are becoming important tools that aid the design of agricultural management schemes and the selection of beneficial root traits. However, while benchmarking is common in many disciplines that use numerical models, such as natural and engineering sciences, functional-structural root architecture models have never been systematically compared. The following reasons might induce disagreement between the simulation results of different models: different representation of root growth, sink term of root water and solute uptake and representation of the rhizosphere. Presently, the extent of discrepancies is unknown, and a framework for quantitatively comparing functional-structural root architecture models is required. We propose, in a first step, to define benchmarking scenarios that test individual components of complex models: root architecture, water flow in soil and water flow in roots. While the latter two will focus mainly on comparing numerical aspects, the root architectural models have to be compared at a conceptual level as they generally differ in process representation. Therefore, defining common inputs that allow recreating reference root systems in all models will be a key challenge. In a second step, benchmarking scenarios for the coupled problems are defined. We expect that the results of step 1 will enable us to better interpret differences found in step 2. This benchmarking will result in a better understanding of the different models and contribute toward improving them. Improved models will allow us to simulate various scenarios with greater confidence and avoid bugs, numerical errors or conceptual misunderstandings. This work will set a standard for future model development.

Keywords: benchmark; call for participation; functional-structural root architecture models; model comparison; root water uptake.

Figure 1

Example of root images used for the benchmarking dataset. (A) Shows an image of lupin root systems, 11 days old, growing in an aeroponic setup. (B) Shows an image of a maize root system growing on filter paper (5 days old). All images were analyzed using the semi-automated root image analysis software SmartRoot (Lobet et al., 2011), colors distinguish different root orders. The RSML files containing the full information about the root systems are provided on the github repository in the folder “M1.1 RSA calibration\M1.1 Reference data.”

Figure 2

Presentation of the data analysis pipelines used for the benchmarking of root architecture models. (A,B) Show the first (M1.1) and second (M1.2) benchmark scenarios, respectively.

Figure 3

Results of M2.1: Infiltration into three initially dry soils: sand, loam, and clay.

Figure 4

Results of M2.2: Rate of evaporation with respect to time from sand with J_s,pot = 0 1 cm/d, loam with J_s,pot = 0 1 cm/d, loam with J_s,pot = 0 3 cm/d, and clay with J_s,pot = 0 3 cm/d.

Figure 5

Results of M3.1: Root water pressure head distribution within a single vertical root.

Figure 6

Visualization of the root system of M3.2 with colors denoting (A) root order, (B) root segment age, (C) root water pressure head.

Figure 7

Root hydraulic properties dependency on root type and root segment age.

Figure 8

Results of M3.2. (Left) Xylem pressure in each root segment of a root system with constant hydraulic properties. (Right) Xylem pressure in each root segment of a root system with age-dependent hydraulic properties.

Figure 9

Results of C1.1: Soil water pressure head gradients around a single, transpiring, root at the onset of stress and the time of its occurrence.

Figure 10

C1.2: Root water uptake by a static root system over time. (Left) Visualization of the volumetric soil water content on vertical and horizontal slices through the soil domain and along the root surfaces. (Right) Root water pressure head.

Figure 11

Results of C1.2 for two scenarios, constant and age-dependent root hydraulic properties. (A) Actual transpiration of reference solution. (B) Root water pressure head distributions inside the root system.