REDOX POTENTIALS NEAR THE AERIAL ROOTS OF RHIZOPHORA MANGLE AND AVICENNIA GERMINANS1

Soil redox potentials and pore water sulfide concentrations on a mangrove island in the Belizean barrier reef system were significantly correlated with the presence of the aerial roots of mangrove trees. Sulfide concentrations were three to five times lower near the prop roots of Rhizophora mangle (red mangrove) and the pneumatophores of Avicennia germinans (black mangrove) than in adjacent (? 1 meter away) unvegetated sediment. Soil redox potentials were also significantly higher near the aerial roots. A comparison of the two species revealed that sulfide concentrations in the rhizosphere of R. mangle were as low as that of A. germinans. However, sulfide concentrations in areas occupied by the black mangrove were variable and a function of pneumatophore density. The occurrence of an oxidized rhizosphere around the roots of both species suggests that the adult trees are equally capable of exploiting reduced sediments as long as their respective pathways for root aeration are functional. RHIZOPHORA MANGLE L. and Avicennia germinans (L.) L. are dominant mangrove species of neotropical intertidal regions where they sometimes occur in monospecific zones. In the Caribbean region, R. mangle is typically found in regularly flooded intertidal areas and A. germinans in areas farther inland at higher ele