Simulating three-dimensional structure, growth and development of rice plants

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Rice productivity is influenced by morphological traits that depend largely on environments and genotypes. The present study aimed to develop a model that simulates rice plant structure, development and growth as affected by climatic factors and cultivation practices. The overall model has not been completed but we developed the submodels of phenology, leaf appearance, tillering, stem elongation, spatial distribution of organs, and light environments in the canopy. The leaf appearance model based on developmental stage and temperature was tested with the field observations in Toyama for the past 15 years and explained well the yearly variation in leaf number. Probability of tiller emergence by node position was developed to simulate the effects of temperature and plant spacing. Based on the morphological data of Koshihikari obtained in Kyoto and Sapporo, we observed that variation in lamina length between locations, years and N levels was small in leaves that appeared before panicle initiation and became progressively larger thereafter. The effect of elevated CO_2 was different among genotypes. Genotypic variation in lamina dimension was marked in length : breadth ratio, but the lamina area could be estimated by a product of length, breadth and a constant (0.75) for various genotypes. Three-dimensional shapes of lamina could well be approximated by 12 triangles, which were used to simulate light environments in the rice canopy. The effects of leaf N and CO_2 were incorporated into the photosynthesis model. These findings provide us with a tool to assess canopy photosynthesis depending on the structure and environments of the canopy.