Ammonium Nitrogen Tolerance Research On Submerged Plant-Myriophyllum Aquaticum

Water eutrophication generated a lot of negative factors adverse to the growth of submerged plants.It has become a common understanding that the increasing of ammonium-N concentration has been an important factor leading to death of submerged plants in typical eutrophic lakes.Currently,studies at home and abroad concerning toxic effect of submerged plants mostly focused on plants which have a lower tolerance of ammonium-N.This subject made a comparative study of physiological responses of three submerged plants under ammonia stress by constructing the micro environment.Then Myriophyllum aquaticum was taken as the main research subject to investigate toxicity effect and peroxidation damage of M.aquaticum under high ammonium-N concentrations and to analyze the toxicity threshold of different tissues.This study was conducted to explore nitrogen metabolism and differences of regulation enzyme activity of M.aquaticum under various degrees of ammonium-N concentrations,to discuss detoxification mechanisms of submerged plants with higher tolerance of ammonium-N under high ammonium-N concentrations and to help us recognize decline mechanism of submerged macrophytes and develope restoration and rehabilitation of submerged macrophytes in eutrophic lakes.The test results were as follows: 1.negative growth of biomass and decreasing of total chlorophyll content appeared in common submerged plants like C.demersum and M.spicatum in 10 mg L-1 ammonium concentration test groups while relative growth rate and total chlorophyll content of M.aquaticum increased with the ammonium concentration increasing from 1 to 20 mg L-1.Ammonium ion N poisoning was associated with the destruction of N metabolism and decrease of the C reserves and soluble protein in the submerged plants.M.aquaticum tolerates NH4+ ion toxicity fairly well by regulating C-N metabolism and transforming excess NH4+against internal physical damage.2.growth rate and total chlorophyll content decreased and the level of membrane lipid peroxidationin of M.Aquaticum increased in 80 mg L-1 ammonium concentration.Negative growth of biomass and poisoned root tissues appeared with exacerbated antioxidant defense system damaged when the concentration of ammonium nitrogen increasing to 120 mg L-1.The tolerance degree of M.Aquaticum in root tissue was higher than that in leaf tissue.Nevertheless,toxiceffect of M.Aquaticum in root tissue was obvious in 120 mg L-1 ammonium concentration.3.as a species tolerant of NH4+stress,M.aquaticum could use nitrogen efficiently which was closely related to key enzymes of nitrogen metabolism.The detoxification-recovery reaction and nitrogen deficiency stress seem closely related to the high-quality AS and NR enzyme activities in M.aquaticum.Ammonium addition had a significant effect in activities of nitrogen metabolism enzymes.GS and AS were inhibited in M.aquaticum by long-term ammonium addition in the 120 mg L-1ammonium-N treatment.M.aquaticum has an effective metabolic regulation pathway to achieve detoxification of ammonium toxicity which seems distinct from that in sensitive species and the key enzymes regulating the nitrogen metabolism of M.aquaticum have obvious differences in tissues.