Symposium-in-Print: Ultraviolet Radiation and Terrestrial Ecosystems Introduction Ultraviolet Radiation and Terrestrial Ecosystemsy

We are pleased to bring this Symposium-in-Print on Effects of Ultraviolet Radiation on Terrestrial Ecosystems to the readers of Photochemistry and Photobiology. Six of the 10 articles contained in this Symposium-in-Print are based on invited presentations given at the symposium on ‘‘Effects of Ultraviolet Radiation on Terrestrial Ecosystems,’’ held during the American Society for Photobiology (ASP) Meeting in Seattle, WA on 10–14 July 2004. One of the articles is based on a presentation given at a symposium on ‘‘Solar UV Radiation Effects on Plants: Interactions with Abiotic and Biotic Stress Factors’’ held at the 13th International Photobiological Congress in San Francisco, CA on 16 July 2000 and two of the articles are based on presentations given at the ASP Symposium on ‘‘Effects of Ultraviolet Radiation on Terrestrial Ecosystems’’ in Baltimore, MD, MD on 5–9 July 2003. One of the invited papers was not presented at an ASP Symposium but was included because of its timeliness and relevance. This Symposium-in-Print is the second in the series of papers published in this journal on Ultraviolet Radiation and Terrestrial Ecosystems during the past 2 years. The first Symposium-in-Print was published in the May 2004 issue of Photochemistry and Photobiology (1). The present ASP Symposium was held to provide a current perspective of research findings obtained since 2000. Partial funding for both the current and previous ASP Symposium was provided by the ASP and the Beltsville Area Director’s Office, Beltsville Agricultural Research Center, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, MD. The articles presented in this Symposium-in-Print address both basic and applied aspects of UV research on terrestrial organisms and cover a range of topics that should be of broad interest to photobiologists, plant physiologists and other researchers. The biological impact of stratospheric ozone depletion, brought about by inadvertent release of chlorofluorocarbons and other trace gases, and the attendant increase in biologically effective ultraviolet radiation on terrestrial and aquatic ecosystems has been of keen interest to researchers and policy makers since the late 1960s (2,3). Changes in stratospheric ozone levels and/or biologically effective ultraviolet radiation (UVBE) have been recorded at a number of locations (4,5,6). Although the UV-B spectral band (280–315 nm) contributes less than 2% of the shortwave radiation received at the earth’s surface, it is of critical importance to terrestrial species (7). Two generalizations are beginning to emerge from field experiments conducted in natural and cultivated ecosystems. The first is that both ambient UV-B (7–10) and ambient UV-A (8,9,11) seem to have a measurable effect in reducing plant growth, especially in the case of herbaceous plants. The second is that changes in ambient UV-B levels may exert a large impact on interactions between plants and phytophagous insects (7,12–15). Numerous studies have been published on the effects of ambient and enhanced UV-B radiation on terrestrial organisms (16–39). One of the major constraints to understanding the mechanisms that mediate the effects of ambient UV-B radiation is the fact that most studies conducted at the molecular level have been carried out in the laboratory using monochromatic UV-B sources (7) or under controlled environments in which the ratio of UV-B to photosynthetically active radiation (PAR) is unrealistically high (40). It is often difficult to compare results because of technical difficulties in predicting, measuring and applying realistic UV-B levels; differences in irradiation protocols in field, greenhouse and growth chamber experiments; and failure to provide adequate levels of PAR and UV-A radiation (40). In their invited review article, Furness and her coworkers (41) describe a number of experimental and analytical approaches that have been used to study the influence of enhanced solar UV-B radiation on plant competition. These include inverse yield-density models and allometric, neighborhood or size structure analyses that provide links between plant and ecosystem responses. They point out that these approaches differ in their abilities to extract information regarding competitive interactions and their morphological underpinnings. Relatively few studies have been carried out * To whom correspondence should be addressed: Sustainable Agricultural Systems Laboratory, Animal and Natural Resources Institute (ANRI), Agricultural Research Service, U. S. Department of Agriculture, Building 001, Room 140, BARC-West, 10300 Baltimore Avenue, Beltsville, MD 20705-2350, USA. Fax: 301-504-8370; e-mail: [email protected] Presented in part at the 32nd Annual Meeting of the American Society for Photobiology, 10–14 July 2004, Seattle, WA. 2005 American Society for Photobiology 0031-8655/05