| Lake eutrophication is considered to be an important reason for the decline of submerged plants,but the mechanism is not clear.At present,most of the researches are focused on the degradation of submerged plants by high ammonia or low light and the combination of these two factors.But few researches on the eutrophication water derived substance sulfide to submerged plants.In this study,Vallisneria Spinulosa as a typical submerged plant was taken as an example to analyze the effects of different concentrations of sulfide on its growth and physiology.In order to further elucidate the mechanism of degradation of submerged plants in eutrophic lakes,the outdoor simulation experiment was designed by orthogonal experiment to explore the acute and chronic combined effects of sulfide,high ammonia and low light on the growth and physiology of V spinulosa.The main conclusions are as follows:1.When the concentration of sulfide is less than 0.05 mmol/L,it is beneficial to the accumulation of biomass of V.spinulosa.It is not conducive to the accumulation of biomass when the concentration of sulfide is higher than 0.10 mmol/L,and the biomass have decreased with the increasing concentration of sulfide.Higher than 0.20 mmol/L of sulfide makes the plant shorter,which has an impact on its growth and development.The long-term treatment of sulfides above 0.50 mmol would exceed the tolerance range of V.spinulosa,deepen the degree of membrane lipid peroxidation,damage the antioxidant system,decrease the resistance to stress or even die.The results of targeted energy metabonomics analysis based on MRM showed that the addition of sulfide could affect the content of ATP(adenosine triphosphate)and the main pathway of its production by inhibiting the energy metabolism pathway.In addition,under the treatment of high concentration of sulfide(0.50?1.00 mmol/L),the roots of V.spinulosa were black and rotten,and the leaves were loss of green even withered gradually.This is similar to the symptoms found in the failure of ecological restoration project in eutrophic lakes.2.The experiment of acute stress showed that low light,high ammonia and sulfide all had effects on the growth and physiology of V spinulosa,and sulfide was the main driving factor.More than 0.10 mmol/L sulfide can inhibit the synthesis of chlorophyll and thus hinder the progress of photosynthesis.2 mmol/L sulfide can seriously hinder the progress of photosynthesis and destroy its antioxidant system,leading to the reduction of plant stress resistance.Under the environment of 2.00 mmol/L sulfide,5%light intensity and 0.50 mg/L ammonia for a long time,it may be lack of material and energy due to the obstruction of photosynthesis,and it is difficult to survive due to the serious decline of stress resistance.3.32d chronic trial finding,the roots of V.spinulosa were black and rotten,and the leaves were loss of green even withered under 2.00 mmol/L sulfide.The concentration of 2.00 mmol/L sulfide would inhibit the photosynthesis of V spinulosa,reduce its biomass,and lead to SOD activity,MDA content,GSH content,total protein content and cytochrome c oxidase activity of V.spinulosa decreased sharply,and made their leaves turn yellow,roots turn black and rotten gradually until the whole plant withered even died.The growth and biomass accumulation of V spinulosa were good in the environment of 0.10 mmol/L sulfide concentration,100%light intensity and 2.00 mg/L ammonia concentration,and the chlorophyll content was the highest in this environmentas in the environment of 0.10 mmol/L sulfide,5%light intensity and 1.00 mg/L ammonia,while the conditions of 2.00 mmol/L sulfide,4.00 mg/L ammonia and 5%light intensity were not conducive to the biomass accumulation.The above research provides a new research perspective and research basis for further clarifying the mechanism of large-scale decline of submerged vegetation in eutrophic shallow lakes. |
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