WATER RELATIONS IN THE SOIL-PLANT SYSTEM:

!

WHAT CAN WE LEARN FROM FUNCTIONAL-STRUCTURAL

PLANT MODELS

guillaume.lobet@ulg.ac.be @guillaumelobet

Plant PhysiologyULg

Guillaume Lobet PhytoSYSTEMS, University of Liège

SEB Manchester - 04th of July 2014

Illustration: Lore Kutschera

WATER IS CENTRAL IN AGRICULTURE

• Farming accounts for 70% over worldwide water use !

• Global changes reduce water availability

!

• Better water use at the crop level (agricultural practices)

!

• Better water use at the plant level (physiology, genetics)

Photo credit: Viewminder @ Flickr

3

WATER MOVEMENT IN THE SOIL-PLANT SYSTEM

Plant PhysiologyULg

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4

WATER FLOW IN THE SOIL-PLANT SYSTEM IS A PASSIVE PROCESS

Plant PhysiologyULg

Air

Leaf

Stem

Root

Soil-0.2

-0.4

-0.5

-0.6

-90

MPa

10%

90%

3 x 10¹⁴ l/year [maize]

Water loss is a passive process, driven by

water potential [ψ] differences in the

system

ψ water potential

5

WATER FLOW IS REGULATED AT MULTIPLE SITES

Plant PhysiologyULg

CO2

H2O

Stomata closed

Stomata open

gs stomatal conductance

ActivePassive

6

WATER FLOW IS REGULATED AT MULTIPLE SITES

Plant PhysiologyULg

kx axial conductance

Active

Passive

7

WATER FLOW IS REGULATED AT MULTIPLE SITES

Plant PhysiologyULg

kr radial conductance

ActivePassive

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WATER FLOW IS REGULATED AT MULTIPLE SITES

Plant PhysiologyULg

ks soil conductance

Active

Passive

ψxyl ψsoil

ψsoil

Kx

Kx

Kr

Krψxyl

ψxyl ψsoil

Kx

Kr

ψxyl ψsoil

KxKr

ψxylψsoil

ψsoil

Kx

Kx

Kr

Krψxyl

ψxylψsoil

Kx

Kr

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WATER FLOW IS REGULATED AT MULTIPLE SITES

Plant PhysiologyULg

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WATER MOVEMENT IS A COMPLEX PROCESS

Plant PhysiologyULg

Water flow in the SPAC is:

a passive process regulated at multiple sites

active and passive regulation an heterogeneous process in space an heterogeneous process in time

a process occurring at different scales

Systems biology Functional Structural Plant Models

11

MODELLING WATER FLOW IN THE PLANT

Plant PhysiologyULg

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12

PLANT AS A CONNECTED NETWORK

Plant PhysiologyULg Lobet et al. 2014. Ecological Modelling

PlaNet-Maize - functional-structural model - 1000’s of connected articles - regulation at the article level - simplified soil

ELECTRICAL ANALOGY

Plant PhysiologyULg Doussan et al., 2006. Plant and Soil

Jh

(z) = �Kx

� x

(z)�z

Axial flux

Jr

(z) = Kr

[ e

(z)� x

(z)]S

Radial flux

Matricial resolution

Landsberg, J. & Fowkes, N., 1978. Annals of Botany

Fluxes

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WATER FLOW REGULATION BY THE PLANT

Plant PhysiologyULg Lobet et al. 2014. Ecological Modelling

0

0.4

-0.5-3.5water potential (MPa)

mod

ifying

fact

or (-

) 1

Axial resistance

rootshoot

0

0.4

-0.5-3.5water potential (MPa)

mod

ifying

fact

or (-

) 1

Radial resistance

root

shoot

cavitation onset / resorption

stomata closing / opening aquaporin gating / trafficking

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SIZE MATTERS. REGULATION AS WELL.

Plant PhysiologyULg

Col

lar w

ater

pot

entia

l [M

Pa]

-6

-4

-2

0A

Root/shoot surface ratio [-]

Col

lar w

ater

pot

entia

l [M

Pa]

*

* ****

*

*

** ******

** ******

** ******

** * *****

** * *****

** * ** ***

Root/shoot surface ratio [-]

No regulation

0 1 2 3 4Root/shoot surface ratio [-]

Col

lar w

ater

pot

entia

l [M

Pa] *

* ***

********

**

** **

***

*

** ****

**** ****** ** * ****

*** * ** ***

cavitation > 90%

B

0 1 2 3 4

Regulation

-6

-4

-2

0

Root system size is important to sustain the shoot evaporative demand

Regulation of hydraulic properties is critical for water homeostasis

Permanent Wilting Point

100 150 200 250 300

-1.0

-0.8

-0.6

-0.4

-0.2

time [h]

wat

er p

oten

tial [

MP

a]

100 150 200 250 300

0.2

0.4

0.6

0.8

1.0

time [h]

gs [-

]

100 150 200 250 300

0.85

0.90

0.95

1.00

time [h]

Kr [

-]

100 150 200 250 300

0.6

0.7

0.8

0.9

1.0

time [h]

Kx

[-]

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ALL REGULATIONS ARE NOT BORN EQUAL

Plant PhysiologyULg

Xylem potential [MPa]

Mod

ifier

1

0

-1.5 0

inhibited

enhanced - gs has a strong effect - Kr has a moderate effect - Kx has almost no effect

- Simultaneous observation - Interactions between regulations

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INTEGRATING SOIL WATER MOVEMENT

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DOES THE SOIL MATTERS?

Plant PhysiologyULg

Soil

Water potential [MPa]

Cond

uctiv

ity [m

/ se

c M

Pa]

10-10

10-20

10-4 10-2 100

100

soil

plant

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cultivated soils

“When the soil is wet it has little influence on the uptake of water

from it by the plant. When it is dry it has a large influence. When it is neither wet nor dry, the extent of

influence is a matter of controversy.”

Passioura, 1980

drying

Systems biology Functional Structural Plant Models

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MODELLING SOIL-PLANT WATER MOUVEMENTR-SWMS

- functional-structural model - 1000’s of connected articles - explicit 3D soil water movement - no shoot (boundary condition)

Javaux et al. 2008. Vadoze Zone Journal

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SOIL PROPERTIES SHAPE THE WATER UPTAKE

Draye et al. 2010. Journal of Experimental Botany

soil water potential (M

Pa)

Clay Clay-loam Loam

- Same root architecture

- Same hydraulic properties

- Different soil types

- Same initial water content

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SOIL WATER CONTENT SHAPES THE WATER UPTAKE

Javaux et al. 2008. Vadoze Zone Journal

Compensatory uptake

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SOIL WATER DISTRIBUTION SHAPES THE WATER UPTAKE

Lobet et al. 2014. Plant Physiology

0

30

-30

0

10

-10

Relative difference

[%]

0.6

1.2

0

0.18

0.24

0.12

Water content [cm3/cm3]

Radial rootwater flow[cm3/day]

Relative difference

[%]

A B

New variables

Uptake sites

Water potentialSoil water content

3D water flow soil-root domain

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USING FSPM TO ANALYSE EXPERIMENTAL DATA

Transpiration

Root system

Soil properties

Soil water contentVALIDATION

R-SWMS

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USING FSPM TO ANALYSE EXPERIMENTAL DATA

30 1.5

WU [cm³/cm³.d]

-0.80 -0.4

ψ [MPa]WC [%]

400 20

New

variables

Time [day]

1

2

3

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CONCLUSIONS AND PERSPECTIVES

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Plant PhysiologyULg

WATER FLOW IN THE SPAC: WHAT CAN WE LEARN FROM FSPM’S?

FSPM’s are needed to analyse complex systems - sensitivity analysis - counter-intuitive phenomenon

Strong interplay between regulatory element - endogenous - exogenous

Limiting step may vary depending on the scenario

Do not forget the soil!

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QUANTITATIVE DATA ARE MISSING…

Plant PhysiologyULg

Well known, many quantitative data

Very few quantitative data. Cavitation susceptibility curves.

Data only for certain species / root types Data about single roots What about the connections?

Very few quantitative data. Environment responses?

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WHERE DO WE GO NEXT?

Plant PhysiologyULg

Long distance signalling ABA signalling Auxin movement …

Lower scale modelling Radial water movement Lateral root formation ….

Higher scale modelling Integration with crop models ….

ACKNOWLEDGEMENTS

Plant PhysiologyULg

Université catholique de Louvain Xavier Draye Mathieu Javaux Félicien Meunier Vincent Larondelle

UC Davis Valentin Couvreur

INRA Avignon Loïc Pagès Pierre Valsesia

BELSPO Belgian Science Policy

FNRS Fond National de la Recherche Scientifique

All models are wrong but some are useful.

George Box, 1987

Presentation available on figshare

bit.ly/seb-lobet