Nitrogen uptake and storage by free-floating wetland species P.stratiotes L.

Abstract

Contents of nitrogen in the natural components (water, soil and plant) were measured 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 when the concentration of NO₃^-N in water was 0.84 mg/l. Under experimental conditions fresh young plants of Pistia stratiotes were exposed to varying doses of inorganic nitrogen (0.5-50 mg/l) for 45 days at mean temperature of 32°C. Samples were taken during fixed experimental time to determine the nitrogen uptake in the P.stratiotes.  Maximum uptake and accumulation in P. stratiotes root and shoot was 39.55 and 37.95 mg/g respectively after 45 days. The rate of uptake and accumulation was in rising trend from the first day of the Pistia incubation. In another part of experiment no nitrogen was left in the basins of low concentrations (0.5, 5 mg N/l) after 45 days of experiment but at higher concentrations (35,50 mg N/l) significant amount of residual inorganic N was left in the experimental basin. The root and shoot biomass followed a raising trend parallel with nitrogen supply till 15 mg N/l. This was opposite to the relationship between the nitrogen accumulation in the tissues and nitrogen supply in the experimental basins. Though, phosphorus and potassium was added as a supplementary growth nutrient but their accumulation was 63 mg/g and 74 mg/g at 50 and 5 mg/lrespectively.