Résumé
The paper describes the dynamics of nitrogen in different components (water, soil and plants) of Kabar wetland situated in Begusarai district of Bihar. Contents of nitrogen in the natural components were determined and were compared with the rate of uptake and accumulation under the experimental conditions. Physico-chemical characteristics of natural water and of test basins were quite similar. The trend of seasonal variation of NO3- -N in water and total N in soil and P. stratiotes tissue was almost similar but content of nitrogen differed significantly in the different components. The accumulation of nitrogen in the tissues of P. stratiotes was 5 to 15 fold higher than the concentration of nitrogen in the water and 2 to 3 fold higher than the nitrogen content measured in the soil. Maximum accumulation of nitrogen in P. stratiotes was 15.25 mg g -1 when the concentration of NO3- -N in water was 0.86 mg l-1. Under experimental conditions six different nitrogen concentrations were supplied and determined the uptake and accumulation of nitrogen in P. stratiotes. Maximum uptake and accumulation was 82.87 g m-2 at the end of 60 days after starting the experiment but still the rate of accumulation was in rising trend. In another part of experiment no nitrogen was left in the basins of low concentrations (0.5 and 5 mg N l-1) at the end of 60 days of experiment but at higher concentrations (50 and 65 mg N l-1) significant amount of N was left in the test basin. The biomass enhancement was parallel with nitrogen supply till 15 mg N l-1. This was opposite to the relationship between the nitrogen accumulation in the tissues and nitrogen supply in the experimental basins. Though, potassium was added as an essential growth nutrient but its accumulation was 95 g m-2 at 5 mg l-1.