Nitrogen Uptake By Vallisneria Natans And Its Effect On Nitrogen Nutrients In Lake Water

Submerged macrophyte is one of the most important primary productivity in the lakeecosystem, and it can influence the structure and function of lake, and it plays a key role inmaintaining the clear water. Vallisneria natans is one of the most common submerged plants inChina, and it is widely used in ecological restoration of shallow lake ecosystem. Vallisneria natanscan absorb nitrogen nutrients for their growth, and their roots are the main parts of absorption.Nitrate (NO₃^--N) and ammonium (NH₄⁺-N) are the main forms of biological available nitrogensource in the sediment pore water of lakes. In this paper, using stable isotope15N tracer techniqueand simulation experiments, we studied the uptake of NH₄⁺-N and NO₃^--N by roots of Vallisnerianatans respectively, and their relationships with the concentration of nitrogen. And we use theseasonal changes of the biomass of Vallisneria natans and nitrogen nutrients to study theirrelationships.The results showed that the uptake of NH₄⁺-N was significantly higher than that of NO₃^--N.Nitrogen was transferred to shoot after it was absorbed, and the transfer rate of NO₃^--N wasrelatively high. The concentrations of NH₄⁺-N affected the uptake of NO₃^--N significantly. Whenthe concentration of NH₄⁺-N was less than0.072mmol/L, the uptake of NO₃^--N increased with theincrease of NH₄⁺-N, then decreased and then maintained a steady state. The effect of NO₃^--N onthe uptake of NH₄⁺-N by the roots had a similar pattern.The results of Nannan Lake and Yuanmiaoguan Lake in Huizhou West Lake showed that, thebiomass and nitrogen storage of Vallisneria natans varied seasonally, had the highest values insummer. NH₄⁺-N and NO₃^--N concentrations of lake water were negatively, related to the nitrogenstorage in Vallisneria natans, This relationship was positive with TN concentrations. However, allrelationships were not statistically significant. TN concentrations of Nannan Lake andYuanmiaoguan lake which are dominated by Vallisneria natans were lower than that of PinghuLake which had no Vallisneria natans. Our results suggest that the reduction in TN is likely due toreduced sediment resuspension and nutrients release by inhibition of Vallisneria natans Themechanisms need further studies.