The selection of plant species resistant to iron toxicity is important in the ecological rehabilitation of mining areas. The objective of our study was to identify the degree of resistance of the grasses Paspalum densum, Hyparrhenia rufa, and Echinochloa crus-galli to iron toxicity on the basis of physiological and biochemical responses in a nutrient solution. The experiments initially consisted of hydroponic cultivation of the three plant species to evaluate short-term responses at increasing concentrations of Fe-EDTA 0.009 (control), 1, 2, 4, 7, and 9 mM; and afterward by prolonged exposure of the resistant grasses to Fe-EDTA concentrations of 0.009 and 7 mM. Iron concentration increased in the leaves of all species evaluated, showing values above the phytotoxic threshold. P. densum and E. crus-galli were selected in view of their resistance to iron toxicity, evidenced mainly by low malondialdehyde (MDA) values due to mechanisms of tolerance and avoidance. In contrast, H. rufa showed an increase in MDA values and a reduction in gas exchange, revealing considerable sensitivity to iron toxicity. The results showed the potential for using P. densum and E. crus-galli in the revegetation of areas degraded by mining iron.
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