| Comments |
P.1066 left column bottom paragraph: "The diffuse component of global radiation penetrates substantially deeper into the plant canopy than the direct radiation component which produces hard shadows. Depending on the shape and size of their leaves, plants increase the fraction of diffuse radiation in the canopy (e.g., conifer needles or the finely divided leaves of some Mimosaceae). Part of the global radiation reaching the surface is reflected, with plant cover having a considerable influence. The bright leaves of desert shrubs reflect >20% of radiation, a spruce forest only about 10%. Bare soil may reflect up to 30%, and freshly fallen snow more than 80% of the incident radiation. The remainder, the radiation balance, represents the amount of energy absorbed by leaves and whole-plant canopies (see Fig. 12.1, see BNID 113221). During daytime, the radiation balance is always positive, but at night, it is either zero or negative. The radiation balance of plant surfaces can be negative during clear nights, when long-wave radiational losses occur (thermal radiation), causing plant tissue to cool below air temperature." |