South African salt marshes: ecophysiology and ecology in the context of climate change.

Abstract

Abstract This paper reviews the distribution, zonation and ecophysiological tolerances of salt marsh plants in South Africa. In South Africa salt marsh covers 11,788.8 ha with the largest areas occurring in the Berg, Olifants, Orange and Langebaan Estuaries. The changing climate necessitates in-depth studies on the responses of these plants so that we can understand and predict future changes in their abundance and diversity. Responses of salt marsh plants to abiotic stressors are reviewed and it is shown that, on a local ecosystem scale, distribution of species is driven by moisture/inundation levels and salinity gradients. Ecophysiology studies have been completed on at least 15 salt marsh species in South Africa, focusing on the responses of salt marsh plants to various factorial combinations of abiotic stressors. Studies also exist on characterization and zonation of salt marsh habitats and have significantly affected salt marsh management policy. Salt marsh plants respond to osmotic and ionic stress through reduction in growth and increase in root:shoot ratio, ion sequestration and accumulation of ionic and compatible organic solutes for osmoregulation. These responses are similar, whether elicited by soil moisture deficit or salinity, but may vary in intensity. Submergence results in increased cytoplasmic acidosis, membrane lipid peroxidation and a rapid increase in reactive oxygen species. Physiologically, tolerant species respond to submergence by down-regulating metabolism, increased synthesis of antioxidant enzymes and up-regulating compatible osmolytes. This translates into increased species growth. These responses collectively determine salt marsh zonation and are important, especially in the context of climate change.