Physiological effects of ammonia-nitrogen concentrations on Hydrilla verticillata
不同浓度氨氮对轮叶黑藻的生理影响

Physiological effects of NH-4-N concentrations (0.5, 1, 2, 4, 8, 16 mg/L) on Hydrilla verticillata cultured in media were investigated at laboratory conditions. The biomass, chlorophyll contents, soluble sugar contents, protein contents, as well as the activities of superoxide dismutase (SOD), peroxidase (POD) and (GS) of Hydrilla verticillata were analyzed. The results showed that low NH-4-N concentration (0.5, 1, 2 mg/L) could simulate the growth of H. verticillata cultured in media while a NH-4-N concentration of above 4 mg/L would deter the growth of H. verticillata markedly. The plants died within three to four weeks when the concentration of NH-4-N in culture solution reached 16mg/L. The chlorophyll contents and the soluble sugar contents of H. verticillata went up with increase of NH-4-N concentration in low NH-4-N concentration experiments (0.5, 1, 2 mg/L NH-4-N). However, when NH-4-N concentration was above 4 mg/L the contents of chlorophyll and soluble sugar in the 24th d, 32nd d and 40th d sampling decreased noticeably compared to the control experiment. In low NH-4-N concentration (0.5, 1, 2 mg/L) experiments the protein contents of H. verticillata decreased initially and increased later; in control experiments the protein content went up continuously; in high NH-4-N concentration (8, 16 mg/L) experiments the protein content decreased remarkably. Overall, the activities of GS, POD and SOD showed no difference in their changing trends; these enzymatic activities increased noticeably under the condition of high concentration of NH-4-N and showed a pattern of initial increasing and subsequent decreasing with activities peaking in the sixteenth or the twenty-fourth day. The results indicate that the increased NH-4-N concentrations were a stress to H. verticillata under eutrophic condition. The increased NH-4-N concentrations could affect the physiological function of H. verticillata, by restraining its growth, and even resulting in its death. Although H. verticillata could resist the changes in NH-4-N concentrations to some extent, its tolerance gradually weakened with time.