Mathematical and computational methods for functional-structural plant modelling using L-systems and their applications to modelling the kiwifruit vine

摘要

Mathematical and computational modelling provides a framework within which the understanding of plant growth and development can be further advanced. By abstracting from reality, it provides a way to test our hypotheses of the behaviour of real plants, offers simple explanations of observed phenomenon, and allows us to make quantitative predictions under new conditions. In particular, functional-structural plant models are well suited for these types of studies, because they capture the complex interactions between plant architecture and physiological processes as governed by the environment. The aim of this research was to investigate and develop mathematical and computational methods for use in functional-structural plant modelling, and, in particular, to allow easy incorporation of various aspects of plant growth and development at different spatial and temporal scales into one complex dynamical system. To this end, a functional-structural kiwifruit vine model was constructed using an L-system based plant modelling platform. The model was used to integrate the kiwifruit vineu27s architectural development with mechanistic modelling of carbon transport and allocation. The branching pattern was captured at the individual shoot level by modelling axillary shoot development using a discrete-time Markov chain. An existing carbon transport-resistance model was extended to account for several source/sink components of individual plant elements. The model was then interfaced with the light simulation program QuasiMC, and used to estimate the absorbed irradiance of each leaf during the course of the vineu27s development. Furthermore, the operation of QuasiMC was illustrated and analysed using an abstract virtual canopy (a triangle mix) and the kiwifruit vine model as examples. Several simulations, inspired by biological experiments, were performed to illustrate the capabilities of the kiwifruit model, including the plastic response of shoot growth to local carbon supply, the branching patterns of two Actinidia species, the effect of carbon limitation and topological distance on fruit size, and the complex behaviour of sink competition for carbon. The model was able to represent the major features of kiwifruit growth and function, and provided a solid foundation for investigating plant modelling methodology. A major challenge in functional-structural plant modelling is the integration of several previously modelled aspects of plant function into one model. To meet this challenge, the kiwifruit model provided the inspiration for extending L-systems with a new modules of modules approach, which combines pseudo-L-systems with sets of productions and lists of modules to consider within those sets. Using the new approach, a model of a kiwifruit shoot was constructed that integrates previously modelled aspects of the shootu27s architecture with carbon dynamics, apical dominance and biomechanics. In the short term, the kiwifruit model will be used to help explore the vineu27s physiology and genetic control. For example, it will help give a physiological interpretation of experimental results on competition for carbon between vegetative and reproductive components of the vine. In the long term, it will serve as the basis for development of decision support systems to help improve kiwifruit production.