GreenLab Course
Principles
Growth cycles
GreenLab model growth and development cycles.
Growth dynamics
A discrete Model
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The GreenLab model evaluates plant structure and production at regular thermal time periods.
The unit time cycle, defined from an average daily temperature sum ratio, is called a growth cycle (CG for or cycle of growth).
The growth cycle value, is usually low compared to a shoot development cycle (under ideal temperature conditions, typical values range from a couple of days for a seasonable plant to several weeks for temperate trees).Hence:
* Thermal time implicitly controls the plant develoment rate (organogenesis).
* Thermal time implicitly controls the duration of organ functioning and expansion.
* However, organ growth does not depend on the temperature, but only on the available biomass to be shared with the other organs.
Growth and development cycle: principles
* For each growth cycle, the model defines organogenesis evolution on a representative of each metamer organ cohort (since all organs in a given cohort share the same chronological and physiological properties).
* Biomass production is computed from organ sources and sizes (usually the functional leaf areas).
* If organogenesis occurs, the different organ cohorts are updated, according to micro and macro state evolutions.
* Biomass demand is then evaluated, for each organ cluster, according to its sink value.
* The remaining pool of biomass is then divided among the available functioning organ clusters, as a proportion if the demand exceeds the pool.
* Organ sizes are computed from their chronological age, their expansion state, and allometry rules
* The remaining biomass, if any, is kept in the biomass pool.
The GreenLab dynamic model cycle (Drawing P. de Reffye, CIRAD)
For each growth cycle:
- 1 - Plant production is computed and stored in the common biomass pool
2 - Organogenesis is computed with potentially new organ cohorts
3 - Plant demand is evaluated and the required biomass split among the organs in proportion to their sink and to biomass availability