Effects of planting densities on water quality improvements and Pontederia cordata's physiology.

Various planting densities (5, 10, or 20 plants per tank) of Pontederia cordata were water-cultivated in purifying tanks to treat polluted water. Seasonal effects of the planting densities on the water quality improvement and the morphology and physiology of the plant were analyzed. Results indicated that planting densities affected the nitrogen and phosphorus removal of water, and the morphology and physiology of plants, including activity of peroxidise and catalase, content of chlorophyll and soluble protein (SP), the length of root, stem and leaf, tiller number and root density. When planting density increased from 10 to 20 plants per tank, the morphology and physiology of plants, and the nitrogen and phosphorus removal by plants improved slowly, but caused a tiller number decline in individual plants. This variation was significant in autumn, and associated with seasonal variations of plant physiology. During autumn, there were 26 tillers in each plant with 10 plants per tank, compared to 14 tillers per plant with 20 plants per tank. Increase in the nitrogen and phosphorus contents of the plants for 5-10 plants per tank was 5.41 and 0.79 g kg(-1), compared to 1.17 and 0.12 g kg(-1) for 10-20 plants per tank, respectively.