GRAAL: a model of GRowth, Architecture and carbon ALlocation during the vegetative phase of the whole maize plant: Model description and parameterisation

A model has been developed to understand the interactions between morphogenetic and carbohydrate partitioning processes during the vegetative development of individual maize plants. It merges models of plant morphogenesis and models simulating the growth of plant compartments as related to assimilate availability. Using object-oriented methods, knowledge is formalised at the object level (local rules of organ development), which has its own properties, and the behaviour of the system arises from interactions between the objects and the integration of the processes into the whole system. Shoot and root organs are initiated as a function of temperature. Their potential growth in size (length, width, diameter) and dry mass depends on temperature and carbon availability. Using the source–sink concept, effective organ growth at each time step (1 day) is calculated from potential organ growth rate and plant carbon availability. Early simulation results indicate that the model makes it possible to reproduce the main features of plant functioning (e.g. kinetics of root:shoot ratio, changes in priority between organs, periods of plant sensitivity and plasticity to carbon availability) and to analyse the sensitivity to the model parameters. The model is shown to be a useful tool for testing functioning hypotheses and for hierarchizing ecophysiological processes involved in stand development.