Response of mangrove plant species to a saline gradient: Implications for ecological restoration

Abstract

Mangroves are salt tolerant plants that occur in tropical and sub-tropical sheltered coasts. Saltwater intrusions into terrestrial landscapes often occur due to either anthropogenic reasons or natural calamities such as tsunamis. We investigated the potential of using mangrove species for rehabilitation of high saline environments by revealing the capacities of species to remove salt from sediment. We established the salt retention capacity of common mangrove species in Sri Lanka i.e., Rhizophora apiculata, Rhizophora mucronata, Ceriops tagal, and Avicennia marina through exsitu and in-situ measurements of NaCl content in plant tissue and soil samples, by titrating with 0.01 N AgNO 3. The results revealed A. marina to be the most efficient in retaining salt within plant tissues while C. tagal is superior to R. mucronata but inferior to A. marina in performing this function. These findings were further confirmed by measuring salt uptake rates of hydroponically grown seedlings of the same species. Although R. mucronata is the most popular species used for restoration, A. marina appears the most suitable mangrove species not only for coastal mangrove restoration but also for rehabilitating salinity affected landscapes.

Spatial distribution and dynamics of selected mangrove forests on the east and west coasts of Sri Lanka

“…A. marina and R. mucronata were found to survive in a wide range of soil salinity (de Silva and Amarasighe 2021a) and it influences the natural distribution of mangrove species (Ball 1998, Barik et al 2017, De Silva and Amarasinghe 2021a. Results of the current study corroborate this observation, i.e.…”

“…Besides, our study revealed that salinity of the substrate influences plant biomass or the standing stock of mangrove vegetation, manifesting the effect of salinity on mangrove plant growth and net primary productivity. Increased soil salinity elevates salt content in mangrove plant tissues that decreases water availability causing a decline in productivity (Lovelock et al 2006;Gilman et al 2008;Osland et al 2014;de Silva and Amarasinghe 2021a). As such, our results suggest that local changes in salinity influence the species composition and hence the spatial distribution of mangroves across the island.…”

“…The spatial distribution and vegetation structure of mangroves in different localities are influenced by many factors such as temperature, precipitation, freshwater runoff, erosion/sedimentation rates, aridity, salinity, nutrient inputs, and ocean circulation pattern (Gilman et al 2008;Osland et al 2017;De Silva and Amarasinghe, 2010;Record et al 2013;de Silva and Amarasinghe 2021a). These factors may largely determine the floristic and faunistic composition and the community structure of the mangrove ecosystem (Cintron et al 1985;Cintron and Novelli 1984).…”