Effects of elevated ultraviolet radiation and endophytic fungi on plant growth and insect feeding in Lolium perenne, Festuca rubra, F-arundinacea andF-pratensis

Plants of perennial ryegrass (Lolium perenne L.), red fescue (Festuca rubra L.), tall fescue (F. arundinacea Schreb.) and meadow fescue (F. pratensis Huds) were exposed at an outdoor facility located in Edinburgh, UK to modul ated levels of UV-B radiation (280-315 nm) using banks of cellulose diaceta te filtered UV-B fluorescent lamps that also produce UV-A radiation (315-40 0 nm). The plants were derived from a single clone of each species and were grown both with and without colonization by naturally-occurring fungal end ophytes. The UV-B treatment was a 30% elevation above the ambient erythemal ly-weighted level of UV-B during July to October. Growth of treated plants was compared with plants grown under elevated UV-A radiation alone produced by banks of polyester filtered lamps and with plants grown at ambient leve ls of solar radiation under banks of unenergized lamps. At the end of the t reatment period, sample leaves were collected for feeding trials with the d esert locust Schistocerca gregaria (Forsk). The UV-B treatment produced no effects on the aboveground biomass of any of the four grasses. The UV-B tre atment and the UV-A control exposure both increased plant height and the nu mber of daughter plants formed by rhizome growth in F. rubra. There were si gnificant effects of endophyte presence on the total fresh and dry weights of F. arundinacea and F. rubra, on fresh weight only in F. pratensis, and o n the fresh and dry weights of inflorescence in F. arundinacea and L. peren ne. There were no effects of UV treatments on the absolute amounts of leaf consumed or on the feeding preferences of locusts for leaves with or withou t endophyte in three species: F. rubra, F. arundinacea and L. perenne. In F , pratensis there was no effect of UV treatment on the weight of leaves con sumed but a significant UVxendophyte interaction caused by a marked change in feeding preference between leaves with and without endophyte that differ ed between the UV-B treatment and UV-A control exposures. The alkaloid comp ounds known as lolines were analysed in leaves of F. pratensis arid were on ly found in plants grown with endophyte. However, there was no significant relationship between total loline content and insect feeding preference. Th ese effects illustrate the potential complexities of species interactions u nder increasing levels of UV-B. The experiment also demonstrates the import ance of appropriate controls in UV lamp supplementation experiments for int erpretation of both plant growth and insect feeding effects. (C) 2001 Elsev ier Science B.V. All rights reserved.