P absorption and removal mechanism of new Salix clone (A42)on eutrophic water with different P concentrations

Phosphorus is the necessary element for plant growth, and its concentration is one of the main indices for water eutrophication. Hence, it is significant to understand how woody plants purify phosphorus in eutrophic water. The purpose of this study is to reveal the P absorption and removal mechanism of Salix matsudana in eutrophic water with different P concentration. We selected new S. matsudana clone (A42) as experimental material and set three levels of P concentration (low P: 0.1, 0.2 mg·L^-1; medium P: 1.0, 2.0 mg·L^-1, high P: 10.0 mg·L^-1), and the floating bed hydroponic experiment was conducted at the greenhouse from July to September, 2017. We found that S. matsudana efficiently removed P in water (removal rate >79% in 21 days). There was a positive correlation between the removal quantity and P concentration in the water. The removal ratio rose at first and then fell with increasing P. Owing to the purification of S. matsudana, the P concentrations ranging from 0.1 mg·L^-1 to 1.0 mg·L^-1 were reduced to minimum threshold concentration of eutrophication (0.016-0.032 mg·L^-1) in seven days. The percentage of phosphorus input in water that assimilated by S. matsudana ranged from 29.0% to 66.9%. The quantity and ratio of assimilated P were respectively positive and negative relation with P concentration. Salix matsudana adapted to eutrophic water with different P concentrations and normally grew during experiment period, with root-shoot ratio being significantly increased with decreases of water P concentrations. The characteristic of phosphorus distribution in plant organs was: stem> leave>root, while the translocation factors (TF) of nitrogen and phosphorus were both greater than 3. When S. matsudana grew in eutrophic water with high phosphorus concentration, the TF of nitrogen and phosphorus significantly increased to 4.53±0.24 and 4.92±0.62 respectively. Our results indicated that S. matsudanais could purify the eutrophic water and it could normally grow. New clone of S. matsudana could effectively absorb phosphorus in the water and accumulated it in the stem, which could reduce secondary pollution. In conclusion, S. matsudana could be used for a short-term treatment on the eutrophic water with low P concentration, while for the long-term treatment it is adapted to eutrophic water with high phosphorus concentrations.