The root system as a hydraulic architecturePrinciples and applications- Principles and applications -

HYDRUS Workshop 2013, Prague

Valentin Couvreur, Félicien Meunier, Jan Vanderborght & Mathieu Javaux

Earth and Life Institute - Environmental SciencesEarth and Life Institute Environmental Sciences

The hydraulic soilThe hydraulic soil--plant system :plant system :

ContextContext –– Principles Principles –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

The hydraulic soilThe hydraulic soil plant system :plant system :

Plant root system impacts : Drying pattern of the soil Plant water availability ??

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Crop yield & soil water storage

Physical principles behind water transport in plants :Physical principles behind water transport in plants :

Context Context –– PrinciplesPrinciples –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

Physical principles behind water transport in plants :Physical principles behind water transport in plants :

- Water is passively driven through plants by a water potential differenceplants by a water potential difference between the soil and the leaves

- This process can be described by physical equations of water flow through radial and axial conductances

- This network of conductances is called the plant hydraulic architecture

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DoussanDoussan detailed root water uptake modeldetailed root water uptake model ((DoussanDoussan et alet al 19981998))

Context Context –– PrinciplesPrinciples –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

DoussanDoussan detailed root water uptake model detailed root water uptake model ((DoussanDoussan et al., et al., 19981998))

- 3D root architectureImposed transpiration

Plant collarater potentialre

ss

- Water flow inside the root (xylem) :

water potentialSt

with Kx = Axial conductance [cm4.hPa-1.day -1]dψxylem = Water potential difference [hPa]

[cm3.day -1]Jx = – Kx . dψxylem / d

- Water flow at the « soil - root » interface :

ψxylem p [ ]d = Distance [cm]

J L ( ) Aptak

e

with Lr = Radial conductivity [cm.hPa-1.day-1]ψ = Water potential [hPa]A R [ 2]

[cm3.day -1]Jr = Lr .(ψsoil – ψxylem ) . A

oot w

ater

up

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A = Root segment area [cm2]

4

Ro

RSWMS : Coupling soil and root water flowRSWMS : Coupling soil and root water flow ((JavauxJavaux et alet al 20082008))

Context Context –– PrinciplesPrinciples –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

RSWMS : Coupling soil and root water flow RSWMS : Coupling soil and root water flow ((JavauxJavaux et al., et al., 20082008))

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Simple physicalSimple physical root water uptake modelroot water uptake model (Couvreur et al(Couvreur et al 20122012))

Context Context –– PrinciplesPrinciples –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

Simple physical Simple physical root water uptake model root water uptake model (Couvreur et al., (Couvreur et al., 20122012))

- We analyzed the structure of analytical solutionsof water flow equations in a simple root system andof water flow equations in a simple root system and extended it to any root system

- Conceptually, root water uptake (RWU) can be considered as the superimposing of two independent processes :

Standard RWU Compensatory RWU

RWU K HT +RWU = Kcomp . - Hs eq . Tact . +

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Standard sink fraction distribution

Standard sink fraction distribution

Soil water potential distribution

Simple physicalSimple physical root water uptake modelroot water uptake model (Couvreur et al(Couvreur et al 20122012))

Context Context –– PrinciplesPrinciples –– Applications Applications –– ConclusionConclusion & perspectives & perspectives

Simple physical Simple physical root water uptake model root water uptake model (Couvreur et al., (Couvreur et al., 20122012))

- We analyzed the structure of analytical solutionsof water flow equations in a simple root system andof water flow equations in a simple root system and extended it to any root system

- Conceptually, the plant collar water potential (Hcollar) can be considered as Stress

the sum of two independent terms :

Charge loss Equivalent soil water potential in root system

H + HTactHcollar = + Hs eq

act

Krs

.

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Standard sink fraction distribution

Soil water potential distribution hyp. 2

Estimation ofEstimation of KK by using preby using pre--dawn potential measurementsdawn potential measurements

Context Context –– Principles Principles –– ApplicationsApplications –– ConclusionConclusion & perspectives & perspectives

Estimation of Estimation of KKrsrs by using preby using pre dawn potential measurementsdawn potential measurementsHs eq

Tact

Krs

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Estimation ofEstimation of KK by using light transmission imaging databy using light transmission imaging data

Context Context –– Principles Principles –– ApplicationsApplications –– ConclusionConclusion & perspectives & perspectives

Estimation of Estimation of KKcompcomp by using light transmission imaging databy using light transmission imaging data

Light Transmission Imaging setup Water content data

Root architectureRoot architecture

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Image: Guillaume Lobet

Estimation ofEstimation of KK by using light transmission imagingby using light transmission imaging

Context Context –– Principles Principles –– ApplicationsApplications –– ConclusionConclusion & perspectives & perspectives

Estimation of Estimation of KKcompcomp by using light transmission imagingby using light transmission imaging

Relative Root Length Densitydistribution (rRLD)

Standard Sink Fraction distribution (SSF)

Requires: RLD measurement Requires: Full root architectureRequires: - RLD measurement Requires: - Full root architectureRequires: - Root ages and typesRequires: - Root hydraulic properties

Can we approximate the SSF by the rRLD when estimating K ?

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Can we approximate the SSF by the rRLD when estimating Kcomp ?

Estimation ofEstimation of KK by using light transmission imagingby using light transmission imaging

Context Context –– Principles Principles –– ApplicationsApplications –– ConclusionConclusion & perspectives & perspectives

Estimation of Estimation of KKcompcomp by using light transmission imagingby using light transmission imaging

Can we approximate the SSF byCan we approximate the SSF by the rRLD when estimating Kcomp ?

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Conclusions :Conclusions :

Context Context –– Principles Principles –– Applications Applications –– Conclusion & perspectivesConclusion & perspectives

RWU model & water stress functionb d th h d li hit t h

Conclusions :Conclusions :

based on the hydraulic architecture approach

S . V = Tact . SSF + Kcomp .(Hs – Hs eq) . SSF (L3.T-1)

H H T / KHcollar = Hs eq - Tact / Krs (P)

Hs eq = Hs · SSF (P)

FeaturesAccurate as compared to Doussan RWU modelAs fast as Feddes RWU modelNumerical / empirical parameterizationClear distinction between stress and compensatory RWU processes

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p y p

Thank you for your attention !

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Sensitivity analysis ofSensitivity analysis of HH llll to RWU parametersto RWU parameters

Context Context –– Principles Principles –– ApplicationsApplications –– ConclusionConclusion & perspectives & perspectives

Sensitivity analysis of Sensitivity analysis of HHcollarcollar to RWU parametersto RWU parameters

What is the impact of an error ofWhat is the impact of an error of Kcomp when predicting Hcollar ?

What about considering SSF equal to rRLD ?

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