[Effects of water-salt stresses on seedling growth and activities of antioxidative enzyme of Suaeda salsa in coastal wetlands of the Yellow River Delta].

The halophyte Suaeda salsa is the pioneer plant and is used for the degraded coastal wetland in Yellow River Delta. The water-salt stress is the most important factor for ecological restoration to degraded coastal wetland. To understand the adaptive mechanism of Suaeda salsa to water-salt stresses, the induced effects of different groundwater table depths (0, -10, -20, -30 cm) and salt stress (0%, 1%, 2%, 3%) on seedlings of Suaeda salsa plant were characterized by the growth parameters of plant height, branch number and biomass of different organs and biological indices of leaf chlorophyll content, the activities of SOD, CAT, the leaf content of MDA and protein. The results showed the significantly (p < 0.001) decreased height of the seedlings from -30 cm to 0 cm of groundwater table depth, together with the decreased the number of branches, the biomass of leaf, shoot and root. The highest total biomass of single plant was (1.09 +/- 0.15) g under the condition of -30 cm water table depth and 0% salt stress. However, the combination of 0 cm water table depth and 3% NaCl resulted in the biomass of (0.23 +/- 0.01) g, which was ca. 21% compared with the highest biomass. Similarly, the contents of leaf chlorophyll a, b and carotenoid were the highest under the condition of -30 cm water table depth and 0% salt stress and lowest under the condition of 0 cm water table depth combined with 3% NaCl. The activities of SOD, CAT were increased significantly (p < 0.05) depending on the increase of salt stress. At 0 cm water table depth, the activities of SOD were 55.00 U/mg with 0% NaCl and 151.58 U/mg with 3% NaCl, respectively. The activities of SOD were decreased when the water table depth increased. However, the activities of CAT achieved the highest level at -30 cm water table depth. At 0 and -10 cm water table depth, the MDA content increased with the increase of salt stress. The MDA content was 0.26 mmol/g at -30 cm water table depth with 3% NaCl, which was approx. 28%-40% of the MDA contents compared with that caused by other salt stresses. These results demonstrated that Suaeda salsa plant could change its morphological characteristics, biomass allocation, and the activities of antioxidative enzymes to adapt severe environment.