Uptake of ammonium by Vallisneria natans and Myriophyllum spicatum under light and dark regimes

The uptakes and removal effects of ammonium nitrogen(NH+4-N) by Vallisneria natans and Myriophyllum spicatum under light(50μmol/(m2·s)) and dark regimes were investigated in a laboratory experiment,with external NH+4-N concentrations at 0,0.01,0.1,1 and 10mg/L.The results showed that the absorption rates of NH+4-N by V.natans and M.spicatum increased with external NH+4-N concentrations and peaked at 1mg/L,and then decreased at 10mg/L.The absorption rates of NH+4-N by the same plant species in the light condition was not less than those in the dark condition.The absorption rate of NH+4-N by M.spicatum was not less than that by V.natans in the same light regime.Under dark regimes,with external NH+4-N concentrations at 1mg/L,the absorption rates of NH+4-N by M.spicatum was 2.42-fold higher than that of V.natans.Under light regimes,with external NH+4-N concentrations at 1 and 10mg/L,the absorption rates of NH+4-N by M.spicatum was 2.47-fold and 1.79-fold higher than that of V.natans,respectively.Therefore,at a certain range of NH+4-N concentrations that macrophytes can tolerate,M.spicatum should be considered as the pioneer species for the restoration of macrophytes in eutrophic lakes.