Nitrogen and phosphorus removal and morphological and physiological response in Nymphaea tetragona under various planting densities

Various planting densities (5, 10, or 20 plants per tank) of Nymphaea tetragona were water-cultivated in nine tanks to treat polluted water. The effects of planting density on nitrogen and phosphorus removal and on plant physiology in various seasons were analyzed. The results indicated that an increase in planting density improved the removal of nitrogen and phosphorus from polluted water. When planting density increased from 10 to 20 plants per tank, the rates of nitrogen and phosphorus removal increased slowly, but some decline in individual plants was observed. The removal of nitrogen and phosphorus from polluted water correlated with seasonal variations in plant physiology, being most significant in autumn. There were 20 tillers in each plant with 10 plants per tank, compared to 11 tillers per plant with 20 plants per tank. The nitrogen and phosphorus contents of the plants for 5-10 plants per tank was 5.2 and 0.52 g kg(-1), compared to 1.2 and 0.13 g kg(-1) for 10-20 plants per tank, respectively. It is important to choose a reasonable planting density that is based on seasonal variations in plant physiology for the ecological restoration of polluted water.