Ecosystem Effects of Solar UV-B not Mediated by Higher Plants
Although the considerable emphasis on UV-B effects on plants and plant-mediated ecosystem effects is deserved, elevated solar UV-B radiation may affect ecosystem function through other mechanisms (Fig. 3.1). Direct effects of solar UV-B on terrestrial animal life, microbes and the lower atmosphere (Chapter 6) all can have important ecosystem-level implications. Comparatively little study has been directed to effects on animal life apart from humans (Chapter 2).
It has been experimentally established that animals, from fish to mammals, can acquire skin cancer under laboratory conditions and some domestic animals exhibit such symptoms in poorly pigmented body areas (Chapter 2). However, in nature, protection by fur and plumage or behavioral patterns make it unlikely that there will be sufficient UV-B radiation exposure for skin cancer to be a hazard for most animals. There is a possibility of eye damage in animals, but that has not been investigated under field conditions.
Microbes exposed to sunlight play important roles in many ecosystem functions including decomposition of plant litter, diseases of plants and animals, biogeochemical transformations (Chapter 5), etc. Microbes in several habitats are exposed to sunlight including those that are airborne, or live on soil, litter and foliage surfaces. Gehrke et al. (1995) found that among fungi in plant litter, Mucor hiemalis and Truncatella truncata were reduced in abundance by UV-B radiation corresponding to pronounced ozone depletion, while Penicillium brevicompactum was unaffected by increased UV-B radiation exposure. Cyanobacteria growing on soil surfaces may be important for nitrogen fixation from the air. It is known that their sensitivity to UV-B radiation also varies considerably among species (see Chapters 4 and 5). Leaf surface microorganism assemblages have also been shown to be altered by increased UV-B radiation (Newsham et al., 1997).
When the stratospheric ozone is depleted,
solar UV-B penetrates more effectively into the lower atmosphere and can
alter local air pollution (Chapter 6), which, in turn can influence terrestrial
ecosystems. For example, under conditions of substantial ambient NOx
more ozone can be formed in the lower atmosphere due to ozone reduction
in the stratosphere (Chapter 6). It is well known that ambient ozone can
adversely affect higher plants (Manning and Tiedemann, 1995). Other nonbiological
effects of elevated solar UV-B radiation include accelerated photodestruction
of plant litter exposed to sunlight (Chapter 5).