Ten species of tropical grasses, Andropogon gayanus Kunth cv. Planaltina, Panicum maximum Jacq. cv. Colonião, Panicum maximum Jacq. cv. Tobiatã, Chloris gayana Kunth, Eragrostis curvula (Schrad.) Nees, Paspalum notatum Flug. cv. Pensacola, Hiparrhenia rufa (Nees) Stapf., Melinis minutiflora Pal. de Beauv., Brachiaria decumbens Stapf., Brachiaria humidicola (Rendle) Schw. and Lolium multiflorum ssp. italicum var. lema were treated with simulated rain containing 5, 10, and 15 g.m-3 of fluoride, in order to evaluate their relative sensitivity and potential as bioindicator for fluoride under tropical conditions. The plants were cultivated according to standardized techniques for active bioindication. The development of visible damages, the accumulation and distribution of fluoride and the dry weight yield were used to assess the effects of the element on the plants. All studied species showed distinct pattern of fluoride accumulation, fluorine contents above the accepted toxic levels for sensitive species (30 µg.g-1) and a good correlation between fluoride content and the phytotoxicity index, except for Brachiaria humidicola. Chloris gayana and Panicum maximum cv. Colonião were the species that better adapted to the standardized cultivation techniques, based on their growth rates, sprout homogeneity and fast appearance of visible symptoms (chlorosis and necrosis). Fluoride effects on stomatal conductance, CO2 assimilation and dry weight yield were also evaluated in these two species, with potential for bioindication use. The results indicate Panicum maximum cv Colonião as a responsive bioindicator while Chloris gayana as a tolerant species, similarly to L. multiflorum.
accumulation; chlorosis; fluoride; photosynthesis; responsive bioindicator; tolerance
