Comparison of Nitrogen and Phosphorus Uptake and Water Purification Ability of Five Submerged Macrophytes

: Uptake of nitrogen (N) and phosphorus (P) and their purification capacity for five native submerged macrophytes were investigated in laboratory simulated hydrostatic conditions,including Hydrilla verticillata,Vallisneria natans,Ceratophyllum demersum,Myriophyllum spicatum,Potamogeton maackianus.The results indicated that the moisture contents of different submerged macrophytes were almost the same before and after the test,with the range of 89.8%-92.0%.The net accumulated biomass changed from 1.52 g·m-2 to 12.92 g·m-2 among different submerged macrophytes,and the highest net accumulated biomass of Hydrilla verticillata was 8.5 times higher than the lowest plant of Potamogeton maackianus.The N and P contents of five submerged macrophytes ranged from 26.54 to 34.44g·kg-1 and from 2.54 to 4.01g·kg-1,respectively,and the N and P contents of Ceratophyllum demersum were relatively high.Total N and P removal efficiency of different submerged macrophyte treatments had ranges of 63.8%-83.1% and 49.2%-70.8%,significantly higher than those of the CK treatment (39.9% and 36.9%),respectively,and the removal efficiency decreased in the order of Hydrilla verticillata >Ceratophyllum demersum >Vallisneria natans >Myriophyllum spicatum >Potamogeton maackianus.Total N and P removal efficiencies of different submerged macrophyte treatments were significantly correlated with net accumulated biomass,with correlation coefficients of 0.994(P<0.01) and 0.996(P<0.01).The contribution of direct N and P uptake to different submerged macrophytes had the ranges of 1.5%-13.3% and 2.2%-13.2%,and the synergism contribution (deducting self-purification capacity of water) of different submerged macrophytes ranged 22.5%-29.9% and 10.1%-20.6%,indicating that the synergistic effect of submerged macrophytes purification was much more significant than the direct uptake effect in the process of water purification.