Physiological adaptability of three mangrove species to salt stress

The impact of salinity on three arboreal mangrove plants, Sonneratia apetala ( Sa), S. caseolaris ( Sc) and Rhizophora stylosa ( Rs), was studied. The three mangrove species were treated with different salinity levels over a three-month period. The response and adaptation of these three mangrove species to salinity were shown to be different. Net photosynthesis rate, stomata conductance and transpiration rate of leaves decreased and soluble sugar content in leaves increased, with salt concentration in all three mangrove species. The malondial dehyde (MDA) content in stems and leaves of Sa and Sc somewhat decreased when the salinity was lower than 10, but rapidly increased with increasing salt concentration. The MDA content in stems and leaves of Rs increased only when salinity was greater than 40. No changes were observed in the MDA content of roots in the three mangrove species. The adaptabilities of Sa and Sc to salt tolerance were limited. The more salt tolerant the mangrove Rs, the more likely the free oxygen radicals were eliminated through the increase in activity of superoxide dismutase (SOD). Results of this experiment identified salinity levels best suited for the growth and metabolism of the species, which provides information necessary for maintaining mangrove forestation along the South China coast.