<b>Chromatic responses of Salicornia Gaudichaudiana Mog. (Chenopodiaceae) to different levels of UV-B rediation and salinity</b>

Abstract

Although coastal plant communities protect the shorelines from erosion and serve as food source and habitat for a variety of economically important species, the impact of ultraviolet radiation (UV) on salt marshes is poorly understood. During the 2002 summer-autumn, the chromatic responses of seedlings and full-grown Salicornia gaudichaudiana plants were quantified for different levels of UV-B radiation (280-320 nm) in an solar UV-B-exclusion experiment in the field (Pólvora Island salt marsh) and an open garden at Universidade do Rio Grande Campus (Rio Grande, RS, Brazil). The impact of sea salt addition (20 gNaCl l-1) on UV-B radiation responses was also evaluated in the open garden experiment. In the marsh experiment only young sprouts of Salicornia gaudichaudiana had their chlorophyll a concentrations depleted by ambient UV-B radiation (0.2 to 6.5 KJ m-2 day-1; average = 3.1 KJ m-2 day-1). In the open garden experiment, seedlings of Salicornia gaudichaudiana had their chlorophyll a concentration reduced 32% by salt addition but not by UV-B exposition. Overall marsh plants had higher concentration of UV-B absorbing pigments than plants cultivated in open garden. Adult shoots, sprouts and seedlings showed 34% to 188% more UV-B absorbing pigments in Control plots (UV-exposed) than in Mylar (UV-B protected). Although the production of shielding pigments by Salicornia gaudichaudiana is an adaptive response to UV-B radiation, the thickness of epidermic structures seems to explain the distinctive UV-B sensitivity of adult shoots and sprouts. The intensity of salt stress and other physical factors in the marsh environment can strongly affect the pigment composition of Salicornia gaudichaudiana and thus its capability to withstand UV-B radiation rising.