Improvement on tolerance of Spirodela polyrrhiza to ammonia at presence of nitrate

The response of Spirodela polyrrhiza to ammonia with the existence of different concentrations of nitrate was investigated in this study. Four series media with different concentrations of ammonia and nitrate were set up in experiments. The relative growth rate and the frond area of S. polyrrhiza in different conditions were studied. The results showed that the relative growth rate and the frond area of S. polyrrhiza decreased with the increasing concentration of ammonia. The maximum concentration of ammonia that S. polyrrhiza can bear is about #rho#(NH_(4)~(+)-N) of 400 mg·L~(-1) without nitrate. But S. polyrrhiza can bear the concentration of ammonia up to #rho#(NH_(4)~(+)-N) of 500 mg·L~(-1) in the presence of nitrate. The relative growth rate of S. polyrrhiza at high ammonia level [#rho#(NH_(4)~(+)-N)>100 mg·L~(-1)] with nitrate was clearly higher than ones without nitrate. The area of fronds with nitrate was larger than ones without nitrate at higher ammonia level [#rho#(NH_(4)~(+)-N)>300 mg·L~(-1)]. It demonstrated that the presence of nitrate could enhance the tolerance of S.polyrrhiza to ammonia.