Robberecht, R. 1989. Environmental photobiology. Pages 134-154 in K.C. Smith. The Science of Photobiology. Second Edition. Plenum Press, New York, New York, USA.

Introduction. The abiotic and biotic components that make up the surroundings or environment of an organism can exert considerable influence on the effects of light-mediated processes within the organism. Environmental factors such as temperature, the availability of water and nutrients, and interactions with other organisms modify the effects of light-mediated processes within an organism and thereby ultimately affect its growth and survival in the ecosystem. The examination of individual processes involving light allows us to understand the mechanism of these processes within an organism. How radiation is absorbed, what wavelengths are utilized, and what action or effect the radiation elicits in biological systems are questions of primary concern for photobiologists. For example, studies on the absorption of light by chlorophyll and the photochemical reactions of the photosynthetic apparatus are important for understanding the fundamental mechanism of photosynthesis. Important considerations in this mechanism would include the absorption spectrum for chlorophyll and the number of photons required to provide sufficient energy for the light reaction of photosynthesis. Although knowledge of how the photosynthetic mechanism works is essential, this alone does not allow us to predict how the whole organism would respond in nature. This is because the actual capacity of a plant for carbon assimilation and biomass production is determined by the complex interplay of plant genetics and physiology, and the environment. The fundamental nature of processes involving light are not changed, but rather their effect is modified by the way in which the organism interacts with its environment. It is therefore important to consider light-mediated processes in the context of the whole organism and its interaction with the environment. Environmental photobiology thus provides a bridge between the understanding of fundamental processes involving light within an organism and the effects of these processes on the whole organism in the ecosystem.

The spectral distribution and irradiance of incoming solar radiation can be significantly altered in terrestrial ecosystems by the vegetation canopy. Further selective attenuation will occur as radiation penetrates the leaf. Therefore, the position of a plant in a forest canopy or leaves within an individual plant canopy will to a large extent determine the wavelength quality and irradiance available for light-mediated processes. The situation is similar for aquatic ecosystems, where the selective attenuation of radiation by water occurs. Water clarity and the location of aquatic plants and microorganisms are critical variables in this ecosystem.

Environmental photobiology thus involves an understanding of how the general environment alters the radiation regime for organisms as well as how the general environment influences the behavior of the organism in the ecosystem after light-mediated processes have produced an effect. The field of environmental photobiology encompasses a wide variety of topics, ranging from the more simple case of how one environmental factor affects one organism, to the most complex level of the ecosystem where the interaction among species and multiple environmental factors must be considered. An environmental factor that has recently caused great scientific and public concern is the potential intensification of UV radiation on earth due to a partial depletion of stratospheric ozone. Because of the effectiveness of UV radiation to cause damage in biological systems and because this environmental problem is of global concern, it will be used to illustrate many of the aspects of environmental photobiology in this chapter.