Progress in Botany Volume 64, 2003, pp 439-471

Light Heterogeneity and Plants: from Ecophysiology to Species Coexistence and Biodiversity

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Light is produced by changes in the energy level of electrons (when an electron changes from a high-energy, Or excited, State to a low-energy state, Its atom will emit a photon), but its dual nature makes it scientifically puzzling: it moves through space as a wave, but when it encounters matter it behaves like a particle, The quantum (Achenbach 2001). In practice “light” is used for the portion of the electromagnetic spectrum in the vicinity of visible light. In plant biology and ecology, photosynthetically active radiation (PAR), Which essentially coincides with visible light, Is probably the most relevant measure of light. The PAR region is where energy is most abundant (it represents on average 43% of the solar irradiance), And it is strong enough to drive electron transport in photosynthesis, Yet weak enough to avoid excessive damage to biological molecules. However, There exists no worldwide network for PAR measurements like the network of actinometric stations, Where global, Direct, diffuse and reflected solar radiation are measured using unified instruments and methodology and are metrologically based on the world radiometric reference (Ross and Sulev 2000). The dual nature of light, I.e., particle versus wave, Affects the way light in general and PAR in particular is measured. One group of sensors measures energy (e.g., W m−2), The other group quanta (e.g., μmol m−2 s−1).