EFFECTS OF INCREASED SOLAR ULTRAVIOLET-RADIATION ON TERRESTRIAL PLANTS

Physiological and developmental processes of plants are affected by UV -B radiation, even by the amount of UV-B in present-day sunlight. Plan ts also have several mechanisms to ameliorate or repair these effects and may acclimate to a certain extent to increased levels of UV-B. Nev ertheless, plant growth can be directly affected by UV-B radiation. Re sponse to UV-B also varies considerably among species and also cultiva rs of the same species. In agriculture, this may necessitate using mor e UV-B-tolerant cultivars and breeding new ones. In forests and grassl ands, this will likely result in changes in species composition; there fore there are implications for the biodiversity in different ecosyste ms. Indirect changes caused by UV-B-such as changes in plant form, bio mass allocation to parts of the plant, timing of developmental phases and secondary metabolism-may be equally, or sometimes more important t han damaging effects of UV-B. These changes can have important implica tions for plant competitive balance, herbivory, plant pathogens, and b iogeochemical cycles. These ecosystem-level effects can be anticipated , but not easily predicted or evaluated. Research at the ecosystem lev el for solar UV-B is barely beginning. Other factors, including those involved in climate change such as increasing CO2, also interact with UV-B. Such reactions are not easily predicted, but are of obvious impo rtance in both agriculture and in nonagricultural ecosystems.