Optical and physiological properties of a plant canopy

Abstract

The characteristics of masses of leaves should be considered while controlling the light environment for plant production. The term “canopy” is used to express the mass of leaves of multiple plants. The optical characteristics and photosynthetic properties of a canopy are sometimes different from those of a single leaf. One of the most important characteristics of a canopy is that there exists a photosynthetic photon flux density (PPFD) distribution on and within the canopy according to its leaf distribution pattern. In addition, the light spectral distribution within the canopy is different from that outside the canopy, owing to light absorption and reflection by leaves. Moreover, the light-photosynthetic curve of a canopy differs from that of a single leaf, showing higher or no light-saturated points. A basic method for estimating canopy photosynthesis is to sum up the photosynthetic rates of small parts of canopy that are assumed to be under uniform environmental conditions. An extinction coefficient is used to express light attenuation within a canopy as a function of LAI and to estimate average PPFD at each horizontal layer.