Salinity responses in two populations of viviparous Rhizophora mangle L. seedlings

Viviparous seedlings of the red mangrove, Rhizophora mangle L., were collected from adult trees growing in areas of low (5%) and high (36%) surface water salinities, and planted as groups in large rectangular pots and treated with seawater corresponding to the two natural concentrations. Among individuals collected from the same site, growth was significantly enhanced in the low (5%) versus high (36%) salinity treatment. Stem and leaf development exhibited larger differences between high and low salinities than did root growth. Propagules showed no increased capacity for growth when treated with salinities similar to the parent tree environments. Seedlings from the high salinity site exhibited faster growth than those from the low salinity site when treated with low salinity water. However, differences between sites were insignificant in the high salinity treatment. Results are discussed in the context of vivipary as a preconditioning mechanism for salt-tolerance and the general effects of salinity on physiological and possible genetic aspects of early development.