Symposium-in-Print: Ultraviolet Radiation and Terrestrial Ecosystems The Influence of Ultraviolet-B Radiation on Growth, Hydroxycinnamic Acids and Flavonoids of Deschampsia antarctica during Springtime Ozone Depletion in Antarctica{y

We examined the influence of solar ultraviolet-B radiation (UV-B; 280–320 nm) on the growth, biomass production and phenylpropanoid concentrations of Deschampsia antarctica during the springtime ozone depletion season at Palmer Station, along the Antarctic Peninsula. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B either by 83% (reduced UV-B) or by 12% (near-ambient UV-B) over the 63 day experiment (7 November 1998–8 January 1999) when ozone depletion averaged 17%. Plants growing under near-ambient UV-B had 41% and 40% lower relative growth rates and net assimilation rates, respectively, than those under reduced UV-B. The former plants produced 50% less total biomass as a result of having 47% less aboveground biomass. The reduction in aboveground biomass was a result of a 29% lower leaf elongation rate resulting in shorter leaves and 59% less total leaf area in plants grown under reduced UV-B. p-Coumaric, caffeic and ferulic acids were the major hydroxycinnamic acids, and luteolin derivatives were the major flavonoids in both insoluble and soluble leaf extracts. Concentrations of insoluble p-coumaric and caffeic acid and soluble ferulic acids were 38%, 48% and 60% higher, respectively, under nearambient UV-B than under reduced UV-B. There were no UVB effects on concentrations of insoluble or soluble flavonoids. INTRODUCTION Stratospheric ozone depletion by anthropogenic chlorofluorocarbons has led to enhanced levels of ultraviolet-B radiation (UV-B; 280–320 nm) reaching the Earth’s surface (1–3). This increase is most pronounced over Antarctica in the spring where biologically effective UV levels have increased 130% since 1980 (3). While these ozone depletion events are most severe in early spring and are typically centered over the Antarctic continent, the Antarctic Peninsula is also experiencing relatively large increases in biologically effective UV-B. For example at Palmer Station (648469S; 648049W) along the west coast of the Antarctic Peninsula average November UV-B irradiance doubled from 1988 to 1996 (4), and this increase is negatively correlated with atmospheric ozone concentrations (5). Day et al. (6) calculated an average enhancement of 62% in biologically effective UV-B (UV-BBE; using the generalized plant damage action spectrum [7] normalized to 300 nm) attributable to ozone depletion during November and December of 1995–1999 at Palmer Station. Antarctic hair grass (Deschampsia antarctica; Poaceae) and Antarctic Pearlwort (Colobanthus quitensis; Caryophyllaceae), the only two vascular plant species native to Antarctica, appear sensitive to solar UV-B levels during springtime in Antarctica. In a 4-year field study on Stepping Stones, a group of islands near Palmer Station, Day et al. (6,8) manipulated solar UV-B levels around naturally growing mixed populations using filters. They found that ambient levels of solar UV-B consistently reduced growth of D. antarctica and C. quitensis and aboveground biomass production of C. quitensis. Single-season experiments that manipulated solar UVB reaching naturally growing plants (9,10) or potted plants (5,11) revealed that reductions in aboveground biomass may be related to slower leaf elongation rates and shorter leaves. Recently, Xiong et al. (11) examined the growth response of potted C. quitensis to near-ambient and reduced levels of solar UV-B during the 1998– 1999 ozone depletion season. They found that plants exposed to near-ambient UV-B produced 54% less aboveground biomass resulting from a 45% and 31% reduction in shoot and reproductive biomass, respectively, compared with those growing under reduced UV-B. The reduction in shoot biomass was attributed to reductions in leaf elongation, size and longevity and lower leaf production. However, the growth parameters associated with reductions in biomass production of D. antarctica have yet to be examined. * To whom correspondence should be addressed: Department of Biological Sciences, TS-242 Trafton Sciences Center, Minnesota State University, Mankato, MN 56001, USA. Fax: 507-389-2788; e-mail: [email protected] Abbreviations: ANOVA, analysis of variance; HCA, Hydroxycinnamic acids; HPLC, high performance liquid chromatography; LAR, leaf-area ratio; LMR, leaf mass ratio; MeCN, acetonitrile; NAR, net assimilation rate; PAR, photosynthetically active radiation (400–700 nm); RGR, relative growth rate; SLM, specific leaf mass; UV-B, ultraviolet-B radiation (280–320 nm); UV-BBE, biologically effective ultraviolet-B radiation Presented in part at the Symposium on UV Effects in Terrestrial Ecosystems at the Annual Meeting of the American Society of Photobiology in Seattle, WA, on 13 July 2004. 2005 American Society for Photobiology 0031-8655/05