Modelling of canopy structure and nitrogen use in plant communities

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(1) Canopy structure with many species was studied in the Miscanthus sinensis grassland at Kawatabi, Miyagi Pref. There were 13 species with Pteridium, Lespedeza, Smilax, Lysimachia and Arundinella in the middle layrs, and Asterm Lactuca, Potentilla, Carex, Astilbe, Solidago and Hypericum in the lowest layrs. There were strong correlations between total leaf area, photon absorption and the amount of leaf nitrogen in each species. Species comprising the upper layrs had larger leaf area and highter photon absorption averaged over leaf area, but had not higher photon absorption per unit aboveground biomass. Species comprising the lower layrs had high SLA (leaf area per unit leaf mass), which led to their high efficiency of biomass use to absorb photons.(2) A model of photosynthesis was developed to describe the nitrogen economy of the leaf of C3 plants. Photosynthetic proteins were categorised into five groups according to their functions in photosynthesis. The effects of the investment of nitrogen in each of these groups on the maximal rate of photosynthesis and the initial slope of the light-response curve were analyzed. The changes in adaptive significance.(3) Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the distribution of nitrogen among leaves were aso as to avoid mutual shading of leaves. It was concluded that both leaf nitrogen and that the contribution of leaf age increases with the decrease in nitrogen nutrient level.