1. ISLSWG workshop, Turin 18 – 19 May 2015
Multi-scale approach as a prerequisite for modeling bioregenerative LSS: MELiSSA approach
Structure of the presentation:
Introduction: MELiSSA loop – review
Mechanistic models: what it is? How it compares to empirical model?
Mechanistic model of plants for the HPC
L. Poulet, J.-P. Fontaine, C.-G. Dussap
ISLSWG workshop, Turin
18 – 19 May 2015

2. MELiSSA Loop - Brief description of compartments
- MELiSSA loop fluxes must be controlled to provide an adequate environment for each compartment.
- Must be based on known mechanisms and validated equations (Mechanistic models) which could predict the outputs knowing the inputs.
- The constraints on the compartments should be studied in order to control the flux exchanges within the loop.
- MELiSSA: biochemical & genetics understanding -> Higher plant model must be compatible with this approach

3. Functions of cultivar, light, RH, T°, etc.
MELiSSA Approach
5 output variables:
O2 release
CO2 fixation
Dry mass quantity
Dry mass composition
Water transport
Needed to get information on mass & energy fluxes on an overall scale
Functions of cultivar, light, RH, T°, etc.

4. Mechanistic vs. Empirical
Plant
Organs
Tissues
Whole-plant variables
Extra variables
Integration synthesis
Analysis reduction
Level i
Level i-1
Empirical modeling
Mechanistic modeling
Mechanistic vs. Empirical
Mechanistic vs empirical => Description vs comprehension
Mechanistic
- Many levels: Crop, plant, organs, tissues, cells, organelles, macromlecules, molecules and atoms
- Understand & describe the ith level which has some unserstanding&mechanism at lower levels
Deterministic control strategy
Mathematical mechanistic model
-> Elementary phenomena vs empirical approach
 derived from the physics and chemistry governing the process.
Systemic aproach of complex systems with feedback loops
Phenomena from molecular to system level
Elemental scale and then integration
Source: Thornley and Johnson, 1990

5. Mechanistic model Pros Cons More phenomena studied
More possibilities for manipulating & improving system
Identifying knowledge gaps
Stimulation of new ideas for experimental approaches
Many assumptions might induce less good fit of data
Not always practically feasible (time and costs)
- Not always applicable when process not well known and equations cannot be solved
Inspired from Thornley and Johnson, and Mark J. Willis & Ming T. Tham, Advanced Process Control, Newcastle University, 2009

6. Higher Plant Compartment
Higher Plant Chamber, MELiSSA Pilot Plant, Barcelona
Example of HPC
Mechanistic modeling approach of HPC starts with mechanistic modeling of plant growth in reduced gravity environment.
Plants for the MELiSSA loop: bread wheat, durum wheat, soybean, potato, rice, lettuce and root beet

7. Processes within a plant
Light
Atmosphere
Water + minerals
Temperature
Photoperiod
Development,
Architecture &
Morphology
Storage
Growth
Respiration
Photosynthesis
Light interception
Gas exchange
Root absorption
Sap ascent
Xylem Phloem
Processes occurring within a plant during plant growth are complex and of multiple origin: morphology, physical, biochemical
- Necessity to structure the model with modules representing the different processes => multi-scale model
Processes in a plant. Source: P. Hezard

8. Mechanistic model of a plant
Photosynthesis
CO2 absorption
Sugar production
H2O evaporation
O2 release
Water transport
Xylem: Water up
Phloem: Sap down
Xylem - Phloem
Root zone
Water & minerals absorption
Gravitropism
Respiration
Growth: metabolic reactions
Link to biomass
Gravitropism effects
Architecture
Shape & structure
Exchange surfaces
Organ
Cell
Plant
Environment
Light flux
Air: RH, O2, CO2, H2O
Root zone: H2O, O2, minerals
Physical
Biochemical
Morphological
Leaf
Stem
Root
Process
Module
Processes can be divided into 3 categories, corresponding to 3 different scales:
Morphological processes linked to the plant scale: plant architecture and development
Physical processes linked to the organ scale: this module can further be divided into 3 sub-modules corresponding to the leaf, the stem and the root.
gas exchange during photosynthesis, light interception, water movements in the plant and root absorption
Biochemical processes linked to the cell scale: metabolic reactions of plant growth
A fourth big module is the one of the environment, interacting with the three others and changing accordingly.
Equations to describe these phenomena are transfer laws, plant geometry and stoechiometry

9. Conclusion BLSS modeling in MELiSSA Example of Higher Plants
Multi-scale approach – Mechanistic
Necessity of understanding local phenomena
Example of Higher Plants
Multiple processes involved in plant growth
Three main scales identified
Physical, chemical and biochemical: ODEs, sequential simulation, etc.

10. THANK YOU