GreenLab Course
Development
Organ factorisation
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In the GreenLab model, phytomers of the same physiological age and the same chronological age share the same fate
GreenLab organ cohorts
Assumption.
Metamers of the same physiological age and the same chronological age are considered as identical, whatever their positions in the plant structure.
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The set defined by all metamers of the same physiological age p and the same chronological age t
defines organ cohorts Co(p,t), where o stands for the various organs borne by the metamer.
Hence, in a given organ cohort, all organs are of the same type (leaf, internode, flower, etc.) and show the same properties and evolution.
The GreenLab model uses this assumption, evaluating biomass demand and biomass consumption from a single representative of each cohort, multiplied by the number of organs No(p,t) in each cohort Co(p,t).
Compared to process-based models, GreenLab can thus be seen as an extension, defining several cohorts for each organ type instead of a single compartment.
The set of cohorts reflects the establishment of minimal architectural dynamics, restricted to the physiological age and the organ age.
In practice, the cohort chronological age has to be expressed from two dates: the cohort appearance date da and the current date dc. The appearance date must be expressed relatively to the full plant appearance date, while the current date can be expressed relatively to the appearance of the set of organs(i.e. the cohort age).
1. Two cohorts Co(p,da, dc) and Co(p,da+i, dc+i) of the same organ, with the same number of organs, the same physiological age, the same age, but two different appearance dates show different evolutions, since the biomass level availability is not stable during plant development and growth.
2. Theoretically, the cohort definition assumption fails if geometrical or positioning gradients and considered.
However, this drawback can be overcome. In such a case, such as differentiation due to orientation or the cumulated reiteration order, the gradient should be considered as a new typological criterion, that can be indexed by a new variable s; cohorts will thus be indexed by three indexes Co(p,da,dc,s).