Nitrogen partitioning among photosynthetic components and its consequence in sun and shade plants

1. Chenopodium album (a sun species) and Alocasia macrorrhiza (a shade species) plants were grown under various photon flux densities (PFDs) to investigate whether nitrogen partitioning among photosynthetic components was optimized under any light conditions. The amounts of several photosynthetic components of the leaves were determined to examine nitrogen partitioning. 2. For the same PFD, nitrogen partitioning among photosynthetic components was similar in both species, except for leaves of C. album grown at 5% PFD, which showed a markedly smaller fraction of nitrogen in photosystem 1. 3. Optimal nitrogen partitioning among photosynthetic components was estimated for various PFDs using a simulation model of leaf photosynthesis. At any PFD, the actual nitrogen partitioning was very similar to the estimated optimal partitioning. However, partitioning in C. album grown at 5% PFD deviated from the optimum. 4. For both species grown under any light conditions, estimated daily photosynthesis of actual leaves was very close to that of leaves with optimal partitioning. It is concluded that both species achieve nitrogen partitioning leading to nearly maximum carbon gain under any light condition.