Effects Of Simulated Nitrogen And Sulfur Deposition On The Growth And Physiological Ecology Of Aquatic Plant

In the past few decades,with the acceleration of human industrialization and ur-banization,a large amount of nitrogen（N）and sulfur（S）were released by human activi-ties,such as fossil fuel combustion,mining and smelting and other industrial processes,and then entered the ecosystem through dry and wet deposition and surface runoff.The deposition of N and S would lead to acidification of soil,freshwater and marine ecosys-tems,resulting in eutrophication and sulfide pollution.At present,existing studies have focused on the N and S input in aquatic ecosystems and the migration and transfor-mation processes of N and S in aquatic ecosystems,but the response of aquatic plants in this process is relatively scant.In this paper,several common aquatic plant species were selected to study the effects of N and S deposition,N and S enrichment in water and hy-drogen sulfide（H₂S）pollution on their growth and physiological characteristics through controlled experiments.The main research results are as follows:1.Effects of N and S deposition intensity on the growth of three emergent plants Phragmites australis,Typha orientalis and Zizania latifolia were studied.The pH of the deposition solution was used to represent different deposition intensities,simulating the natural deposition frequency and dose,and four deposition intensities were set,namely the control group,low intensity deposition（pH 5.0）,medium intensity deposition（pH3.5）,and high intensity deposition（pH 2.0）.The results showed that medium and low intensity deposition promoted the growth of Z.latifolia and P.australis,while having no significant impact on the growth characteristics of T.orientalis.High intensity deposi-tion reduced the root-shoot ratio of T.orientalis and P.australis.The photosynthetic pigment concentration of T.orientalis and P.australis exhibited their characteristics of“non-affecting”plants,while Z.latifolia was an“inhibitory”plant.Under high intensity deposition,the soluble protein concentration of P.australis and Z.latifolia decreased significantly and the proline concentration increased significantly.Under acid deposi-tion,the MDA concentration of the three emergent plants increased significantly,while the antioxidant enzymes did not change significantly.Acid deposition at low and medi-um intensities promoted the synthesis of non-structural carbohydrates in three emergent plants,but high intensity acid deposition was detrimental to the synthesis and transport of non-structural carbohydrates.Acid deposition also changed the nutrient uptake dy-namics of plants.The ability of the three emergent plants to adapt to N and S deposition was ranked as Z.latifolia>P.australis>T.orientalis.2.To explore effects of N and S enrichment in water on the growth of submerged plant Myriophyllum spicatum and floating-leaf plant Nymphoides peltata,nine N and S gradient treatments(N₀S₀、N₀S₁、N₀S₂、N₁S₀、N₁S₁、N₁S₂、N₂S₀、N₂S₁、N₂S₂;N₀=0.6 mg L^-1,N₁=2 mg L^-1,N₂=4 mg L^-1,S₀=20 mg L^-1,S₁=40 mg L^-1,S₂=60 mg L^-1)were set up in the experiment.The results showed that the high N addition inhibited the plant height,root length,biomass and root C accumulation of M.spicatum,but pro-moted the number of ramet,biomass and accumulation of C in various organs of N.pel-tate.The high N addition reduced the root-shoot ratio of the two plants and increased the specific leaf area and N concentration of each organ of two plants.Synergistic addi-tions of N and S significantly increased the stem and leaf N concentration of two plants.There were significant differences in the concentration and proportion of C,N,P and S among different organs,and there was an asymmetric response strategy with N and S inputs.Compared to N addition,plants were less sensitive to S addition in response.The response rates of two life-form aquatic plants to environmental changes was different,and the submerged plant M.spicatum was more sensitive to the addition of N and S.3.To explore the stress of H₂S on three submerged plants Elodea nuttallii,Hydrilla verticillata and M.spicatum,five NaHS（H₂S donor）gradients（0 m M,0.01 m M,0.1m M,0.5 m M,1 m M）were set up in the experiment.The results showed that the NaHS treatment inhibited the number of ramet of E.nuttallii,but increased the plant height growth of M.spicatum.Low concentrations of H₂S increased the Fv/Fm of H.verticil-lata and M.spicatum,while high concentrations of H₂S stress significantly reduced the Fv/Fm of the three plants.Each NaHS treatment significantly increased the concentra-tion of photosynthetic pigments in E.nuttallii.0.5 m M NaHS significantly increased the MDA,H₂O₂ and soluble sugar concentration of E.nuttallii.Under high H₂S concentra-tions,the M.spicatum had higher SOD and POD activities.S concentrations of H.ver-ticillata and M.spicatum significantly increased in high NaHS treatment.Under the high concentration of H₂S stress,the adaptability of the M.spicatum was the strongest.In this study,several common aquatic plants were selected as research objects by simulating controlled experiments and exploring the important N and S cycle processes in the aquatic ecosystem,including N and S deposition and the resulting N and S en-richment and sulfide pollution.The effects of simulated N and S deposition on the phys-iology and ecology of aquatic plant were discussed by combining morphology,physiol-ogy and constant elements,so as to better understand N and S input and loop process.