Near-red/far-red radiation ratio (NR/FR)

Range direct sunlight 1.2: undergrowth beneath a dense crown 0.2 unitless
Organism Biosphere
Reference Körner C (2013) Plant-environment interactions. Chapter 12, pp.1065-1166 in: Bresinsky et al. (eds) Strasburger's plant sciences. Springer Berlin Heidelberg p.1072 right column 2nd paragraph
Comments P.1072 left column 4th paragraph: "Radiation which has passed through green leaves or is reflected from green structures is enriched in far-red radiation (700–800 nm) and depleted in near-red (620–680 nm), that is, the near-red/far-red ratio (NR/FR e.g., I660/I730) is smaller. The fact that plants by their red-light sensors (phytochrome see >Sect. are able to detect their position relative to neighbors has far-reaching consequences for the development of plant stands and for the competition between plants. It has been shown in experiments with individual plants that runners are able to detect and avoid ‘‘green-occupied’’ places, thereby optimizing plant investment into new growth." P.1072 right column 2nd paragraph: "Regeneration of dense plant stands by seedlings under a closed leaf canopy is influenced by the shift in the spectrum of red light from near red to far red so that germination of viable seeds is only initiated when a gap appears in the crown (a near-red signal), signaling a possibility of gaining assimilates by photosynthesis and therefore of survival. Regeneration of forests by seedlings is thus highly dependent on the dynamics of the canopy (gap dynamics). Independent of the intensity of solar radiation, a dense crown reduces the near-red/far-red ratio from about 1.2 in direct sunlight to 0.2 in undergrowth (>Fig. 12.5). Thus, determination of the NR/FR ratio is a further, indirect method of quantifying canopy density (LAI (leaf area index) see >Sect. 12.1.3)."
Entered by Uri M
ID 113233