Effects Of Three Nitrogen Forms On The Growth And Physiological Properties Of Ceratophyllum Demersum

The effect of three nitrogen forms on growth and physiological index and mechanism of Ceratophyllum demersum were investigated by static laboratory experiment. The purpose of this study is to ascertain the concentrations of three kinds of N-nutrition under which the growth of Ceratophyllum demersum are significantly inhibited and the physiological metabolism is seriously disturbed and to provide scientific basis for using Ceratophyllum demersum to improve water condition. According to the indexes determined in the study ,the conclusions are as follows:(1) The height, the biomass and the survival percentage of Ceratophyllum demersum were not significantly inhibited with increasing concentration of NO3-N.When the concentration of NO3-N was lower than 100mg/L, Ceratophyllum demersum grew normally.(2)The height, the biomass and the survival percentage of Ceratophyllum demersum were significantly inhibited under high concentration of Urea-N. The height of Ceratophyllum demersum decreased; the biomass of Ceratophyllum demersum increased at first but decreased later and the survival percentage of Ceratophyllum demersum decreased with increasing concentration of Urea-N. The Urea-N threshold was about 15mg/L for growing of Ceratophyllum demersum.(3)It was the free ammonia not the total ammonia that inhibits the height, the biomass and the survival percentage of Ceratophyllum demersum in water. When the concentration of free ammonia was higher than 0.41mg/L, the height, the biomass were significantly inhibited and the survival percentage was decreased. The free ammonia threshold was about 0.683mg/L~0.82mg/L for growing of Ceratophyllum demersum.(4)The contents of chlorophyll, MDA and H2O2 of Ceratophyllum demersum increased with increasing concentration of NO3-N. The membrane permeability and O2·ˉproduction rate increased with increasing concentration of NO3-N. The activity of POD increased while the activity of SOD almost unchanged with increasing concentration of NO3-N.(5)The MDA contents and the membrane permeability increased with increasing concentration of Urea-N. The chlorophyll and the H2O2 contents and the activity of POD and O2·ˉproduction rate increased at first but decreased later under high concentration of Urea-N. The activity of POD decreased all the time under high concentration of Urea-N.(6)The membrane permeability and the MDA contents of Ceratophyllum demersum in high free ammonia treatment combinations were much higher than those of other treatment combinations. The O2·ˉproduction rate and H2O2 contents are sensitive to free ammonia and increased at first but decreased later under high free ammonia concentration. The activities of SOD and POD decreased all the time under high concentration of free ammonia.