Morphological, biochemical and physiological responses of a tropical coastal plant Guettarda speciosa to salt stress

Abstract Selection and utilization of plants with high salt tolerance can be efficient to rapidly construct or restore the vegetation of the tropical coral islands. Here, we investigated the response of Guettarda speciosa, a typical tropical coastal plant, to salt stress. Different morphological, physiological and biochemical changes in G. speciosa plants after being subjected to NaCl stress based on the salt content of the reference seawater were studied. The results showed that G. speciosa can be tolerant to 25 g L−1 NaCl which corresponds to 2.5% salt content of seawater. A series of adaptive mechanisms were triggered to cope with salt-stress, including the increase in the thickness of leaf epidermis and palisade tissue to limit water loss, changes in photosynthetic pigments, and antioxidant defense mechanisms. Osmoregulatory substances and antioxidant enzymes worked together to cope with membrane lipid peroxidation caused by the accumulation of reactive oxygen species under salt stress and maintain the stability of osmotic potentials. Our findings indicated that G. speciosa has a strong salt tolerance but probably could not tolerate prolonged seawater immersion, which limit its coastal distribution. Therefore, G. speciosa can be considered for vegetation construction and ecological restoration in tropical coral islands such as those in South China Sea.