Abstract: By using automatically controlled device, a greenhouse mud culture experiment was conducted to study the effects of simulated regular semidiurnal tide inundation on the seed germination and seedling growth of mangrove species Acanthus ilicifolius. The inundation time gradient was installed as 0, 3, 6, 9, 12, 15, 18, 21 and 24 h·d^-1, and the artificial seawater with a salinity of 2‰ was prepared. Some physiological and biochemical parameters, including seed germination rate, seedling height and biomass, leaf area, leaf proline, malonyldialdehyde (MDA), and chlorophyll contents, and leaf superoxide dismutase (SOD) activity were determined.  For the A. ilicifolius, longer term (≥15 h·d^-1) tide inundation delayed the seed germination and decreased the germination rate, while shorter term (<15 h·d^-1) inundation was beneficial to the seed germination. With increasing inundation duration, the leaf proline and MDA contents and SOD activity increased after an initial decrease, while the leaf chlorophyll content decreased gradually. Under ≥3 h·d^-1 inundation, the seedling biomass, height growth, leaf area per plant, and leaf chlorophyll content all had a negative correlation with inundation duration. Under 0-3 h·d^-1 inundation, the total biomass, dry weights of root, stem, and shoot, and leaf chlorophyll content were significantly higher than those in other treatments. In contrast, under ≥18h·d^-1 inundation, the total biomass, leaf area, and leaf chlorophyll content decreased significantly, and the root/shoot ratio increased gradually. In this study, 0-3 h·d^-1 was the optimal duration of inundation for the seedling growth of A. ilicifolius, and 18h·d^-1 was the critical duration. When the inundation duration was ≥18 h·d^-1, the seedling growth was inhibited significantly.

Key words: Constructed wetland, Vertical flow, Downflow-upflow, Wastewater purification