CANOPY STRUCTURE AND PHOTON FLUX PARTITIONING AMONG SPECIES IN A HERBACEOUS PLANT COMMUNITY

This paper demonstrates a new analysis of photon flux partitioning among species and an evaluation of the efficiency of photon flux capturing in terms of biomass investment. For that purpose, distributions of aboveground biomass, leaf area, and photon flux density (PPFD) were determined with the stratified harvest method in a stand of a tall herbaceous community on a floating fen at the time of peak standing crop. The stand contained 11 species and the photon flux absorbed by each species in the stand was estimated. Three tall dominant species absorbed 75% of the incident PPFD, while eight short subordinate species absorbed 2.5%. Tall species in the canopy received higher PPFD averaged over leaf area (Phi(area)). However, the PPFD absorbed per unit aboveground biomass (Phi(mass)) of the tall species was not higher than that of the subordinate species. Phi(mass) is a product of the leaf area ratio (LAR, the ratio of leaf area to aboveground biomass) and Phi(area). There was a trade-off relationship between LAR and Phi(area). To have a high Phi(area), plants place their leaves at higher positions in the canopy, which necessarily decreases LAR. Aboveground biomass was regarded as an investment (cost) to capture PPFD (benefit). Phi(mass), as a ratio of benefit to cost, indicates an efficiency of biomass investment to capture photon flux. Tall species appeared to have an advantage over subordinate species in receiving a large fraction of incident PPFD, while subordinate species have an advantage in efficiently using their biomass to capture PPFD.