[Environmental Effect of Substrate Amelioration on Lake: Effects on Phragmites communis Growth and Photosynthetic Fluorescence Characteristics].

Growth of rooted aquatic macrophytes was affected by the nature and composition of lake bottom sediments. Obviously, it has been recognized as an important ecological restoration measure by improving lake substrate and then reestablishing and restoring aquatic macrophytes in order to get rid of the environmental problem of lake. This study simulated five covering thickness to give an insight into the influence of substrate amelioration on Phragmites communis growth and photosynthetic fluorescence characteristics. The results showed that the total biomass, plant height, leaf length and leaf width of Phragmites communis under capping 5 cm were much more significant than those of capping 18 cm (P < 0.01), at the 120 d, the underground: shoot biomass ratio and fine root: underground biomass ratio were also much higher than those of other treatments (P < 0.05), which indicated that capping 18 cm treatment would significantly inhibit the growth of Phragmites communis , but the growth of control group Phragmites communis was slightly constrained by eutrophicated sediment. In addition, as the capping thickness growing, the underground: shoot biomass ratio of the plant would be reduced dramatically, in order to acquire much more nutrients from sediment for plant growing, the underground biomass of Phragmites communis would be preferentially developed, especially, the biomass of fine root. However, Photosystem II (PS II) photochemical efficiency (Fv/Fm), quantum yield (Yield), photochemical quenching (qP), non-photochemical quenching (qN) of Phragmites communis under different treatments had no significant differences (P > 0.05), furthermore, with much greater capping thickness, the photosynthesis structure of PS II would be much easier destroyed, and PS II would be protected by increasing heat dissipating and reducing leaf photosynthetic area and leaf light-captured pigment contents. In terms of the influence of sediment amelioration by soil exchange on the growth and photosynthetic fluorescence characteristics of Phragmites communis, plant growth could be effectively promoted under capping 2 cm and capping 5 cm by increasing the Eh value and nutrient content, whereas plant under capping 18 cm would be much easier adaptive to low-light stress in winter season, of which capping 2 cm treatment was conducive to enhance the initial slope of RLCs (α), maximum electron transport rate (ETRmax) and minimum saturating irradiance (Ek). With regard to the harness of environmental problem of lake, the eutrophication status of lake will be mitigated by using multi-ecological measures to control the internal nutrients content once the external loading was first effectively controlled.