SIMULATED OPTIMAL STRUCTURE OF A PHOTOSYNTHETIC SYSTEM - IMPLICATION FOR THE BREEDING OF FOREST CROP IDEOTYPE

A single leaf and canopy are two different levels of a photosynthetic system which have the function of carbon fixation and energy balance for plant and crop processes. A mechanistic model was derived to understand the photosynthetically based optimal structure for the maximization of whole-system nitrogen use efficiency. The model is based upon the use of a nonrectangular hyperbola for leaf photosynthetic response to irradiance, the linear relationship of photosynthetic capacity with nitrogen content, and the Monsi-Saeki theory for the light-intercepting characteristics of the system. The whole-system carbon gain is maximized by partitioning of leaf nitrogen content (therefore photosynthetic capacity and other related physiological parameters) in terms of negatively exponential decrease with cumulative leaf area index, which has the same extinction rate with irradiance within the system. The biomass production of the photosynthetically based optimal structure (ideotype) and its relative advantage over uniform structure increase with increasing irradiance, nitrogen availability, and leaf area index. Such properties of ideotypes associated with leaf biology and geometry are discussed. Its well as their application to short-rotation intensive culture in forest crops.