Mobility, bioavailability and distribution of Fe and Cu in mangroves (Avicennia schaueriana and Rhizophora mangle) from a semiarid coast in NE Brazil

Abstract

Mangroves buffer metals transfer to coastal areas though strong accumulation in sediments making necessary to investigate metals’ bioavailability to plants at the rhizosphere. This work evaluates the effect of mangrove root activity, through iron plaque formation, on the mobility of iron and copper its influence on metals’ uptake, and translocation through simultaneous histochemical analysis. The Fe²⁺ and Fe³⁺ contents in porewaters ranged from 0.02 to 0.11 µM and 1.0 to 18.3 µg.l^-1, respectively, whereas Cu concentrations were below the method’s detection limit (<0.1 µM). In sediments, metal concentrations ranged from 12,800 to 39,500 µg.g^-1 for total Fe and from 10 to 24 µg.g^-1 for Cu. In iron plaques, Cu concentrations ranged from 1.0 to 160 µg.g^-1, and from 19.4 to 316 µg.g^-1 in roots. Fe concentrations were between 605 to 36,000 µg.g^-1 in the iron plaques and from 2,100 to 62,400 µg.g^-1 in roots. Histochemical characterization showed Fe³⁺ predominance at the tip of roots and Fe²⁺ in more internal tissues. A. schaueriana showed significant amounts of Fe in pneumatophores and evident translocation of this metal to leaves and excretion through salt glands. Iron plaques formation was essential to the Fe and Cu regulation and translocation in tissues of mangrove plants.

Key words
Bioavailability; iron plaque; metals; porewater; rhizosphere; sediment