WATER RELATIONS IN THE SOIL-PLANT SYSTEM:

Transcription

1 SEB Manchester - 04th of July 2014 WATER RELATIONS IN THE SOIL-PLANT SYSTEM: WHAT CAN WE LEARN FROM FUNCTIONAL-STRUCTURAL PLANT MODELS Guillaume Lobet PhytoSYSTEMS, University of Liège! Illustration: Lore Kutschera

2 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: Flickr

3 1 WATER MOVEMENT IN THE SOIL-PLANT SYSTEM 3

4 WATER FLOW IN THE SOIL-PLANT SYSTEM IS A PASSIVE PROCESS ψ water potential -90 Air 90% -0.6 Leaf MPa Stem Root Soil 10% 3 x 10¹⁴ l/year [maize] Water loss is a passive process, driven by water potential [ψ] differences in the 4 system

5 WATER FLOW IS REGULATED AT MULTIPLE SITES gs stomatal conductance Stomata closed H2O CO2 Stomata open Passive Active 5

6 WATER FLOW IS REGULATED AT MULTIPLE SITES kx axial conductance Active 6 Passive

7 WATER FLOW IS REGULATED AT MULTIPLE SITES kr radial conductance Passive Active 7

8 WATER FLOW IS REGULATED AT MULTIPLE SITES ks soil conductance Active 8 Passive

9 WATER FLOW IS REGULATED AT MULTIPLE SITES Kx Kx ψxyl Kr ψsoil ψsoil Kr ψxyl Kx ψsoil Kr ψxyl Kx ψxyl Kr ψsoil ψsoil Kr ψxyl Kx ψxyl Kx Kr ψsoil Kx ψxyl Kr ψsoil 9

10 WATER MOVEMENT IS A COMPLEX PROCESS 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 10

11 2 MODELLING WATER FLOW IN THE PLANT 11

12 PLANT AS A CONNECTED NETWORK PlaNet-Maize - functional-structural model s of connected articles - regulation at the article level - simplified soil 12 Lobet et al Ecological Modelling

13 ELECTRICAL ANALOGY Axial flux J h (z) = K x x(z) z Radial flux J r (z) =K r [ e(z) x(z)]s Matricial resolution Fluxes Landsberg, J. & Fowkes, N., Annals of Botany Doussan et al., Plant and Soil

14 WATER FLOW REGULATION BY THE PLANT Axial resistance modifying factor (-) shoot root cavitation onset / resorption water potential (MPa) Radial resistance modifying factor (-) root shoot water potential (MPa) stomata closing / opening aquaporin gating / trafficking 14 Lobet et al Ecological Modelling

15 SIZE MATTERS. REGULATION AS WELL. Permanent Wilting Point A No regulation B Regulation Collar water potential [MPa] cavitation > 90% Root/shoot surface ratio [-] Root system size is important to Regulation of hydraulic properties is sustain the shoot evaporative demand critical for water homeostasis 15

16 ALL REGULATIONS ARE NOT BORN EQUAL water potential [MPa] time [h] gs [-] time [h] Kr [-] time [h] Kx [-] time [h] - Simultaneous observation 1 inhibited - Interactions between regulations - gs has a strong effect Modifier - Kr has a moderate effect 0 enhanced - Kx has almost no effect Xylem potential [MPa] 16

17 3 INTEGRATING SOIL WATER MOVEMENT 17

18 DOES THE SOIL MATTERS? Conductivity [m / sec MPa] plant cultivated soils soil 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 Soil a matter of controversy. Passioura, Water potential [MPa] Systems biology Functional Structural Plant Models drying 18

19 MODELLING SOIL-PLANT WATER MOUVEMENT R-SWMS - functional-structural model s of connected articles - explicit 3D soil water movement - no shoot (boundary condition) 19 Javaux et al Vadoze Zone Journal

20 SOIL PROPERTIES SHAPE THE WATER UPTAKE Clay Clay-loam Loam - Same root architecture - Same hydraulic properties - Different soil types - Same initial water content soil water potential (MPa) 20 Draye et al Journal of Experimental Botany

21 SOIL WATER CONTENT SHAPES THE WATER UPTAKE Compensatory uptake 21 Javaux et al Vadoze Zone Journal

22 SOIL WATER DISTRIBUTION SHAPES THE WATER UPTAKE A B Radial root water flow [cm3/day] 1.2 Relative difference [%] Water content [cm3/cm3] Relative difference [%] Lobet et al Plant

23 USING FSPM TO ANALYSE EXPERIMENTAL DATA Transpiration New variables Root system Uptake sites Soil R-SWMS water content Water potential Soil properties 3D water flow soil-root domain Soil water content VALIDATION 23

24 USING FSPM TO ANALYSE EXPERIMENTAL DATA 1 2 New variables 3 Time [day] WC [%] WU [cm³/cm³.d] ψ [MPa]

25 4 CONCLUSIONS AND PERSPECTIVES 25

26 WATER FLOW IN THE SPAC: WHAT CAN WE LEARN FROM FSPM S? Strong interplay between regulatory element - endogenous - exogenous Limiting step may vary depending on the scenario Do not forget the soil! FSPM s are needed to analyse complex systems - sensitivity analysis - counter-intuitive phenomenon

27 QUANTITATIVE DATA ARE MISSING 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? 27

28 WHERE DO WE GO NEXT? Long distance signalling ABA signalling Auxin movement Lower scale modelling Radial water movement Lateral root formation. Higher scale modelling Integration with crop models. 28

29 ACKNOWLEDGEMENTS Université catholique de Louvain Xavier Draye Mathieu Javaux FNRS Fond National de la Recherche Scientifique Félicien Meunier Vincent Larondelle BELSPO UC Davis Belgian Science Policy Valentin Couvreur INRA Avignon Loïc Pagès Pierre Valsesia

30 All models are wrong but some are useful. George Box, 1987 Presentation available on figshare bit.ly/seb-lobet