A study on the response of two mangrove species (avicennia marina and rhizophora mucronata) seedlings to different sulphide and salt concentrations

Mangroves grow in differing salinity regimes from marine to fresh water. Those of the genus Avicennia have salt-excreting glands on the leaves whereas in Rhizophora, which does not have salt excreting glands, the amount of salt entering the vascular system seems to be regulated by mechanism located in roots. The effects of sulphide and salinity on growth of the two mangrove species, Avicennia marina and Rhizophora mucronata were investigated. Plant growth parameters such as height, number of leaves and number of nodes were recorded. In this greenhouse study, it was demonstrated that the growth of seedlings from these species was affected in sediment with high sulphide concentrations (1.5mM NH2S). The height of the two plant species decreased significantly with increasing sulphide concentration with the tallest height found for non-sulphide dosed plants which were 71.2±3.2cm for Avicennia marina and 42.9±2.0cm for Rhizophora mucronata. Highly significant difference was found between control treatment and seawater logged plants of both species of Avicennia marina and Rhizophora mucronata. On contrary no significant difference between the two plant species was found in the number of leaves. Salinity decrease growth and survival of these halophytic plant species. The chloride content of the plants was implicated for the decrease in growth. Sulphide affected both species although Rhizophora mucronata was affected much more and earlier than to Avicennia marina. The conclusion of these results is that high sulphide and salinity in the sediment affect mangrove seedling regeneration and establishment.