Effects of increased solar ultraviolet radiation on terrestrial ecosystems

Elevated solar W-B radiation associated with stratospheric ozone reduction may exert effects on terrestrial ecosystems through actions on plants, micr obes, and perhaps on some animals. At the ecosystem level, the effects are less well understood than at the molecular and organismal levels. Many of t he most important, yet less predictable, consequences will be indirect effe cts of elevated UV-B acting through changes in the chemical composition and form of plants and through changes in the abiotic environment. These indir ect effects include changes in the susceptibility of plants to attack by in sects and pathogens in both agricultural and natural ecosystems; the direct ion of these changes can result in either a decrease or an increase in susc eptibility. Other indirect effects of elevated W-B include changes in compe titive balance of plants and nutrient cycling. The direct W-B action on pla nts that results in changes in form or function of plants appears to occur more often through altered gene activity rather than damage. The yield of s ome crop varieties can be decreased by elevated UV-B, but other varieties a re not affected. Plant breeding and genetic engineering efforts should be a ble to cope with the potential threats to crop productivity due to elevated UV-B. For forest trees, this may be more difficult if effects of elevated UV-B accumulate over several years. All effects of elevated W-B radiation m ust be considered in the context of other climate changes such as increased temperature and levels of carbon dioxide, which may alter the UV-B respons es, especially for plants. The actions of elevated carbon dioxide and W-B a ppear to be largely independent, but interactions occur between changes in W-B and other factors. Other ecosystem-level consequences of elevated UV-B radiation are emerging and their magnitude and direction will not be easily predicted. (C) 1998 UNEP. Published by Elsevier Science S.A. All rights re served.