title: Ammonium, microcystins, and hypoxia of blooms in eutrophic water cause oxidative stress and C-N imbalance in submersed and floating-leaved aquatic plants in Lake Taihu, China.
abstract: The heavy bloom of cyanobacteria is a disastrous consequence of freshwater eutrophication, and the bloom is highly toxic due to its secondary metabolites called microcystins (MCs). The release of organic substances from dense blooms causes an increase in NH4+ and decrease in oxygen in lake water. In the present study, the dynamics of physio-biochemical responses of five aquatic macrophytes to MCs and NH4+ stresses in Meiliang Bay were evaluated. The bay is one of the most seriously eutrophized areas dominated by the toxic cyanobacteria of Lake Taihu, China. The results demonstrate that aquatic macrophytes in Meiliang Bay are subjected to successive external stresses. From January to May, they are subjected to high NH4+ stress (>0.56 mg L(-1)), whereas from June to September or during dense blooms, the macrophytes experience both MC proliferation and moderate NH4+ toxicity (>0.3 mg L(-1)). In August, high NH4+ stress occurs along with hypoxia stress, whereas from September to December, the macrophytes experience moderate NH4+ stress, causing a serious imbalance in C-N metabolism and oxidative stress. Between the two aquatic plant life forms, floating-leaved plants are more resistant to the stresses of eutrophication than are submersed plants. Elevated MCs in the water column can aggravate oxidative stress and suppress the soluble protein contents of aquatic plants. High NH4+ in the water causes severe C and N imbalance in submersed macrophytes because of considerable carbon consumption for free amino acid synthesis. The superoxide dismutase activities of submersed macrophytes are suppressed by low light penetrating the eutrophic water, which might impair the antioxidative function of the plants. The findings of this study provide mainly field evidence that reveals the physical, chemical, and biological stresses on aquatic plants in bloom-prevailed eutrophic lakes.
authors.affiliation: Donghu Experimental Station of Lake Ecosystems, State Key Laboratory for Freshwater Ecology and Biotechnology of China, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
authors.forename: Meng
authors.initials: M
authors.lastname: Zhang
authors.forename: Zhengqi
authors.initials: Z
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
authors.forename: Yaqin
authors.initials: Y
authors.lastname: Liu
authors.forename: Leyi
authors.initials: L
authors.lastname: Ni
authors.forename: Te
authors.initials: T
authors.lastname: Cao
authors.forename: Ping
authors.initials: P
authors.lastname: Xie
mesh_terms: D059001:Aquatic Organisms / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D002244:Carbon / Q000032:analysis / Q000378:metabolism; D057486:Carbon Cycle; D002681:China; D000458:Cyanobacteria / Q000254:growth & development; D004784:Environmental Monitoring; D005068:Eutrophication; D005618:Fresh Water / Q000737:chemistry*; D052998:Microcystins / Q000032:analysis / Q000633:toxicity*; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D058458:Nitrogen Cycle; D018384:Oxidative Stress; D063245:Plant Development; D010944:Plants / Q000187:drug effects* / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000032:analysis / Q000633:toxicity*; D014873:Water Pollutants / Q000032:analysis / Q000633:toxicity*
chemical_list: D052998:Microcystins; D000644:Quaternary Ammonium Compounds; D014873:Water Pollutants; D002244:Carbon; D009584:Nitrogen