COMPARATIVE RESPONSE OF THREE TROPICAL GROUNDCOVERS TO SALT STRESS.

The increasing interest in cultivating groundcover plants in warm and semiarid areas requires a better understanding of the salinity effects on landscape plants. This work aimed to study the response of three groundcovers (Alternanthera dentate, Sphagneticola trilobata, and Alternanthera amoena) to high sodium chloride concentrations. The trial was conducted in the natural greenhouse environment. Plants were raised in pots filling clay-loamy soil. Hewitt's nutrient solution containing 0, 25, 50, 75, and 100 mM NaCl irrigated the plants. Plant growth, antioxidative enzyme activity, and the relative water content (RWC), proline, sodium, potassium, and chloride were determined. The study indicated that increasing NaCl concentration in the nutrient solution led to: a) significant differences in the fresh weight of shoots among salinity treatments and among species; b) increased root growth with increasing salinity stress up to the mild stress level of 25 mM NaCl, however at different rates with three species; c) reduced RWC of the leaves of three species grown under salinity-induced stress; d) the increased proline content of the leaves, and more pronounced increases with A. dentate and A. amoena from 0 to 50 mM NaCl, and with S. trilobata from 0 to 100 mM NaCl; e) significant changes in the activities of antioxidative enzymes including superoxide dismutase, peroxidase, and catalase; f) significant decrease of the K+/Na+ ratio along with increase of salinity stress; g) increased ratio of leaf/root content of Cl- in A. dentate and in particular, A. amoena; h) a significant reduction in visual qualities of all examined plants. Therefore, because of its ability to maintain leaf characteristics, visual quality, and salt-tolerance mechanisms even under high salinity, S. trilobata can be considered for urban landscaping projects in semiarid and saline areas where low-quality water is used for irrigation. [ABSTRACT FROM AUTHOR]