Physiological analyses of Genipa americana L. reveals a tree with ability as phytostabilizer and rhizofilterer of chromium ions for phytoremediation of polluted watersheds

Genipa americana L. is a tree that tolerates soil flooding and high levels of Cr3+, therefore it can be used in recomposition of ciliary forests at chromium-polluted watersheds. In this study, the ability of G. americana to phytoremediate the two major ionic Cr forms was assessed through Cr3+ and Cr6+ speciation, leaf gas exchange, growth and chemical composition of seedlings under Cr3+ and Cr6+ treatments. In greenhouse experiment, 4-month old seedlings were transferred to nutrient solution and, after three months, were submitted to 15 and 30 mg L−1 of each ionic Cr form. After 15-days, leaf gas exchanges were measured and seedlings were sampled for evaluation of growth and chemical composition. Results showed that Cr6+ is fully converted into Cr3+ inside the plant; the absorption of Cr3+ and Cr6+ interfered with the absorption kinetics of Zn, Cu, Fe, K, Mg, Ca and P; increments in nutrient solution of Cr6+ decreased root biomass and of both forms decreased shoot biomass; both Cr ions increased leaf area; mainly the exposure to Cr6+ form decreased net photosynthesis per unit leaf area, stomatal conductance to water vapor and leaf transpiration; and Cr highly accumulated in roots only as Cr3+, independently from the ionic form applied to seedlings. Hence, although exposure to Cr3+ and Cr6+ affected growth and development of G. americana seedlings, this woody species demonstrated a relevant capacity for phytoremediation of chromium, by phytostabilizing Cr6+ and rhizofiltering Cr3+.

► G. americana seedlings accumulate high levels of Cr in their roots. ► All Cr6+ absorbed is converted to Cr3+ inside the plant. ► Exposure to Cr affects leaf-gas exchange and macro/micronutrients of G. americana. ► Roots and/or shoots biomass decreased with exposure to high Cr. ► Leaf number decreased, but leaf area increased with exposure to Cr.