Study On A Structure-function Model Of Plant Growth And Its Calibration

Plant growth simulation model provides a quantitative approach to plant growth study, which involves multidisciplinary expertise: botany, agronomy, silvics, applied mathematics, physics, computer science and so on. In the traditional ecophysiological process-based models plant architecture is oversimplified, and the interactions between plant structure and functioning are not considered enough. Corner-Model plant is simple from an architectural point of view, but its growth obeys the general laws of plant biology. In fact many economic crops belong to this model and some kind of plants of complex architecture can be seen as the stack of Corner-Model structures. In the dissertation, a structure-function model of plant growth was studied, in which Corner-Model plant was taken as the studied object at the level of individual plant and organs. The mathematical behaviors of the model were analyzed, and the calibration of the model was made using the experimental data of plant growth and structure.1. According to the general laws of plant biology, a mechanistic structure-function model of plant growth at the growth cycle level was made in which organs?fresh weights and their geometric sizes were taken as the model variables. This model took into account the interaction between plant structure and physiological functioning and it was able to simulate the development of both topological and geometrical structure at the same time.The organs production has a strong correlation with the accumulated temperature. In the dissertation, this relationship was extended to the pure expansion stage for those plants that have only finite structural elements. Plant water-transpiration was obtained by the hydraulic structure and environmental parameters~ and the water use efficiency gave the fresh matter production that was shared among organs according to source-sink-based allocation rules and organ expansion laws. Then the geometry of the organs was computed according to their allometric rules. The developments of plant topological and geometrical structure changed the hydraulic structure at the same time. So the model included feed-back processes between plant growth, architecture, and functioning in an iterative and cyclic way. Satisfactory results were obtained on single stemmed cotton plant, winter wheat, maize and sunflower.2.The mathematical behaviors of the model for Corner-Model plant were studied. The results of the influence of the model parameters upon plant growth and structure provided effective means to verify the model.IIIABSTRACT3.A global partition model was adopted for the fresh matter allocation among organs by considering all the individual organs at the same level. It was more suitable for the case that plant topological structure of different kind of organs dynamically changed often. The global model overcame the shortcoming of the compartmental one that worked hierarchically with a primarysecondary sink manner.4.The discrete probability density function of beta distributk,n was used to express the organs?expansion laws, which was flexible enough to fit a variety of expai~ion forms. Its integral form that produced a sigmoid curve was used to simulate the phenomenon thai the internode sink strength varies with internode rank.5.To calibrate the model there were two steps needed: firstly the external parameters could be measured directly or could be obtained by simply processing the experimental data, for example, the thickness of the leaf blade. Secondly some special optimization algorithm had to be used to estimate the functional parameters that were hidden behind the measured data.The nonlinear least squares method was adopted for the estimation of hidden parameters, which had good convergence and took very short computing time. An automatic way to compute data weights for multi-target items by standardization was presented. The methods were practically proved effective by applications to cotton, winter wheat, maize and su...