In order to find out the difference in absorbability of different aquatic plants on nitrogen (N) and phosphorus (P) existing in surface water

and even to explore its mechanism

the simulated ditch experiment and pot experiment were conducted using 8 different aquatic plants. And the plants with great difference on absorbing N and P were selected to make further exploration on root physiological characteristics and microbiological changes of sediment. The results showed that the concentrations of N and P in ditch water decreased significantly after planting aquatic plants

among 8 aquatic plants

the greater biomass was observed in Pontederia cordata

watermifoil

Sorbaria sorbifolia

Zizania and thalia dealbata

which could absorb more nutrients

resulting in consequently

the decreased nutrients in ditch water. Compared with the treatment of no aquatic plants

nutrient residual in ditch water decreased significantly

total N decreased by 22.4%~44.0%

ammonium nitrate decreased by 24.5%~36.8%

nitrate decreased by 13.6%~51.6%

total P decreased by 15.6%~34.6% and water-soluble P decreased by 26.3%~41.3%

respectively. Aquatic plants could absorb more nutrients was due to their stronger root activity

more xylem sap or higher SAP nutrient concentration. But these advantages could not exist in one specific aquatic plant

for example

Zizania had the stronger root activity

while the N and P concentrations in xylem sap were higher in watermifoil

Pontederia cordata and Sorbaria sorbifolia. In the ditch water planted aquatic plants

where the decreased proportions of N and P were larger

the total number of microorganisms

nitrobacteria and denitrifying bacteria

even the microbial biomass C

N and P were also higher

and vice versa.