MARSHAL, a novel tool for virtual phenotyping of maize root system hydraulic architectures

Abstract

Functional-structural root system models combine functional and structural root traits to represent the growth and development of root systems. In general, they are characterized by a large number of growth, architectural and functional root parameters, generating contrasted root systems evolving in a highly non-linear environment (soil, atmosphere), which makes the link between local traits and functioning unclear. On the other end of the root system modelling continuum, macroscopic root system models associate to each root system a set of plant-scale, easily interpretable parameters. However, as of today, it is unclear how these macroscopic parameters relate to root-scale traits and whether the upscaling of local root traits is compatible with macroscopic parameter measurements. The aim of this study was to bridge the gap between these two modelling approaches. We describe here the MAize Root System Hydraulic Architecture soLver (MARSHAL), a new efficient and user-friendly computational tool that couples a root architecture model (CRootBox) with fast and accurate algorithms of water flow through hydraulic architectures and plant-scale parameter calculations. To illustrate the tool’s potential, we generated contrasted maize hydraulic architectures that we compared with root system architectural and hydraulic observations. Observed variability of these traits was well captured by model ensemble runs. We also analysed the multivariate sensitivity of mature root system conductance, mean depth of uptake, root system volume and convex hull to the input parameters to highlight the key model parameters to vary for virtual breeding. It is available as an R package, an RMarkdown pipeline and a web application.

Combining cross‐section images and modeling tools to create high‐resolution root system hydraulic atlases in Zea mays

“…The continuous red circles stand for the fully suberized endodermis should keep in mind that the experimental procedure is likely to be more accurate, illustrating the usual tradeoff between precision and throughput. Meunier et al (2020) showed that modifying hydraulic properties changes the root system hydraulic architecture and thus affects the whole root system conductance (K rs ). Tuning root hydraulic conductivity functions to match experimental data or test new hypotheses through simulation studies could therefore show the local impact of root anatomy or cell hydraulic properties on the whole root system conductance.…”

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

“…In analogy to the electric circuit model, Couvreur et al (2012) introduced a reduction of the 3-dimensional root hydraulic architecture to modular macroscopic equations and parameters operational for land surface and crop models (Baram et al, 2016;Sulis et al, 2019). Such a multiscale approach offers to connect the dots between models and measurable hydraulic and geometrical properties from the cell to the plant scale (Couvreur et al, 2018;Passot et al, 2018;Meunier et al, 2019) thus integrating essential processes and functional-structural properties for large scale models.…”

Connecting the dots between root cross-section images and modelling tools to create a high resolution root system hydraulic maps inZea mays

“…In both cases, making free-hand root cross-section takes around 10 to 20 minutes. Meunier et al (2020) showed that modifying hydraulic properties changes the root system hydraulic architecture and thus affects the whole root system conductance ( K rs ). Tuning root hydraulic conductivity functions to match experimental data or test new hypotheses through simulation studies could therefore show the local impact of root anatomy or cell hydraulic properties on the whole root conductance.…”

“…. However many studies that used functional-structural root model to simulate water uptake use the hydraulic conductivity that have been estimated by Doussan et al (1998) , such as in R-SWMS (Javaux et al, 2008) , OpenSimRoot (Postma et al, 2017) or MARSHAL (Meunier et al, 2020) . Although those estimations were groundbreaking for the community at the time, we now need to be able to quantify root hydraulic conductivities that directly match the data that we want to assess.…”

“…Indeed, the radial hydraulic conductivity ( k r ) is a key component of the water absorption and the axial hydraulic conductance ( k x ) defines the water transport along the root (Leitner et al, 2014) . Changes in the local root hydraulic properties, at the cell and organ scale, are known to have global repercussions on the root hydraulic behavior (Tardieu et al, 2018;Meunier et al, 2020) and are considered as important breeding targets to create drought resilient varieties (Maurel and Nacry, 2020) . The quantification of root hydraulic conductivity along the roots is therefore needed to have a quantitative understanding of the root water uptake dynamics.…”