Functional analysis of canopy structure of grasslands

点击翻译按钮获取中文摘要

1. Canopy structure was studied in the following grasslands : flood plain vegetation of River Rhein (Amerongen), pasture (Molenpolder), chalk grassland (Limburg), floating fen (Westbroek) and Miscanthus sinensis grassland (Kawatabi). In each vegetation, distribution and partitioning of photon flux density (PPFD), leaf area, biomass, and nitrogen among species were determined.2. Tall dominant species in a 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. Aboveground biomass was regarded as an investment cost to capture PPFD (benefit). PHImass, as a ratio of benefit to cost, indicates an efficiency of biomass investment to capture photon flux. Tall species 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.3. Photon absorption per unit leaf nitrogen (PHI_N) was determined for each species to indicate in situ PNUE (photosynthetic nitrogen use efficiency). Both tall dominant species and short subordinate species could have high PHI_N, but through different processes : high PHI_N of dominants resulted from high PHI_<area>, while high PHI_N of subordinates resulted from low n_L (nitrogen concentration per unit leaf area).4. Light-saturated CO_2 exchange rates per unit leaf area (CER) and per unit leaf nitrogen (potential PNUE) was determined. Species with high CER and high n_L had low potential PNUE, while species with low CER and low n_L showed high potential PNUE. Nitrogen use efficiency (NUE) was also evaluated as a reciprocal of plant nitrogen concentration. Three measures of NUE showed strong conformity. It was concluded that NUE of subordinate species was as high as or even higher than that of dominant species.