:distribution Of Submerged Plants In Hongze Lake And Nansi Lake And The C-N Metabolism Of Dominant Species

Hongze Lake and Nansi Lake are important water resource regulators on the east line of the South-to-North Water Diversion Project. In this study, the plant composition and dominant species, including the temporal and spatial distribution of dominant species, in these lakes were investigated. The dominant submerged plant species in the two lakes were chosen to study the effects of different nitrogen resources composition and exogenous carbon addition on the plant’s C-N metabolism.In Hongze Lake, a total of 14 species of aquatic plants were identified, belonging to 10 families and 11 genera. The dominant species are Potamogeton crispus L, Potamogeton pectinatus L, Nymphoides peltatum(Gmel.) O. Kuntze. The annual water level fluctuation of Hongze Lake was more than 100 cm, and the transparency was between 14.7±5.3 cm and 40.5±13.0 cm. it was supposed that the huge water level fluctuation and the low transparency lead to the dominance of the Canopy-forming submerged plants and the floating-leaved macrophytes.In Nansi Lake, a total of 18 species of aquatic plants were identified, belonging to 11 families and 13 genera. The dominant species are Potamogeton crispus L, Potamogeton. pectinatus L, Myriophyllum spicatum L and Nymphoides peltatum(Gmel.) O. Kuntze. The submerged plants took the advantage of aquatic plants in all sampling sites. The floating-leaved macrophytes and free floating macrophytes were less than the submerged plants in both species and distribution.The C-N metabolic characteristics of three submerged plants, Myriophyllum spicatum L, Elodeo canadensis Michex and Ceratophyllum demersum were studied under different C(NH4-N): C(NO3-N) ratios with 2 mg/L of total dissolved inorganic nitrogen. The addition of NH4-N lead to significant increase of free amino acids(FAA) content in three species, and the FAA content reached the maximum under condition of 2 mg/L NH4-N. Meanwhile, significant differences of soluble carbohydrate(SC) existed among three species, and two-way ANOVA analysis revealed that specie difference contributed 69% to the differences of SC. When NH4-N was totally replaced by NO3-N, SC/FAA ratio in three species significantly increased. C(NH4-N): C(NO3-N) ratios contributed 56% to the differences of SC/FAA ratio.Effects of inorganic carbon and NH4-N additions on C-N metabolism in Potamogeton crispus were studied.Results show that HCO3- addition buffered the p H elevation of the system. Under high ammonia condition, the addition of HCO3- led to increase of SC content, which may alleviate the ammonia stress to plant. P. crispus could survive under high ammonia concentration, which may be one of the reasons that it is generally dominant species in the eutrophication lakes。...