Example d’exercie pour le modèle MARSHAL. Exemple créé par Valentin Couvreur et Valentine Calay (Faculté des bio-ingénieurs, UCL)

Petite vidéo explicative sur MARSHAL:

The context

Following the success of your research on the root permeability of millet, Syngenta hires you as a consultant to integrate the “root hydraulics” component into soybean ideotypes (Glycine max). An ideotype is a conceptual plant that brings together the characteristics (or traits) ideally suited to a soil x climate combination.

Root traits:

Syngenta would like to test a priori the drought tolerance of future soybean varieties with increased root radial conductivity (0.000281 instead of 0.000181 cm hPa-1 d) in the young area of each root type (0 -> 9 cm from the tip). These features are called RT (high radial conductivity in young taproot tissue), RLL (high radial conductivity in young long lateral root tissue), and RL (high radial conductivity in young lateral root tissue).

Varieties with early maturity of the root xylem can also be selected. These have an axial conductance multiplied by 10, 9 cm from the tip of the root. These features are called XT (high axial conductance in young taproot tissue), XLL (high axial conductance in young long lateral root tissue), and XL (high axial conductance in young lateral root tissue).

The environment:

Soil evaporation in the arid climate of the Negev Desert generates a water potential on the soil surface of -15000 hPa (“permanent wilting point”), but the underground microirrigation system linearly increases the water potential to -300 hPa (“field capacity”) at 40 cm depth. Drainage naturally stabilizes this potential at -300 hPa below 40 cm.

Questions :

  • For the default root system, what are the root types that absorb the most water (root depth profile / radial fluxes tab), and what is the root type that carries the most water in its xylem (root depth profile / axial fluxes tab)?

  • Under the evolution / Transpiration simulations tab, you can see how the water availability for the plant (considered equivalent to its transpiration) responds to the environment and root traits. Among the features XT, XLL, and XL (modified one by one), which is the most promising to increase water availability? Interpret.

  • Among the traits RT, RLL, and RL, which most increases water availability for the plant? Interpret.

  • You can now conclude which radial and axial conductivity traits should be selected as a priority for your ideotype.

  • How does the water availability for this ideotype evolve in the presence of a surface micro-irrigation system (water potential of -300 hPa at the surface, decreasing linearly to reach -20000 hPa at 40 cm depth, and keeping this value of -20000 hPa at greater depth)?

  • Under these conditions, what is the water availability of the initial variety compared to the variety with the RT trait? Interpret.

A hybrid analytical-numerical method for solving water flow equations in root hydraulic architectures.
Meunier F, Draye X, Vanderborght J, Javaux M, Couvreur V.

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