Effect And Mechanism Of Sodium Nitroprusside On The Absorption Of Eutrophic Substances In Water By Water Hyacinth

Eutrophication of water bodies remains an urgent environmental problem that needs to be solved.Among many restoration methods available,the restoration method of aquatic plants is widely used due to its low cost,good effect,and aesthetic advantages.To ensure the successful completion of restoration project,the selection of plants used for restoration is crucial.Water hyacinth（Eichhornia Crassipes）is recognized as an advantageous species in the restoration of eutrophic water bodies due to its fast absorption rate of nutrients and strong adaptability to the environment.However,its rapid growth and reproduction can cover the water surface and damage the aquatic ecosystem.Therefore,water hyacinth is usually only used for the restoration of small to medium-sized enclosed water bodies.Researchers have shown that nitric oxide（NO）is an important signal molecule in plant cells,participating in seed germination,plant growth and development,and nutrient absorption,etc.Therefore,in this study,sodium nitroprusside（SNP）（the widely used NO donor）was used to treat water hyacinth.The effects of different concentrations of SNP on the absorption of nutrients,the growth and development of water hyacinth,and root nitrogen（N）assimilation of water hyacinth in different eutrophic water bodies were investigated.The effects of decomposition products of SNP on the nitrogen assimilation and the growth and development of water hyacinth were evaluated.The aim was to find the SNP dosage that could enhance its purification capabilities while avoiding the negative impacts of water hyacinth,and reveal the effect mechanism of SNP improving the absorption of water hyacinth on nutritents in water body.The main results are as follows:（1）The dosage of SNP promoting the absorption of water hyacinth on N in water and increasing the requirement amount for N of water hyacinth was explored.After comparing the N uptake patterns of water hyacinth from natural water and shaded water（eliminating the interference from algae）,it was found that compared to the single group of water hyacinth,1μM SNP promoted the root growth of water hyacinth and increased its uptake rate of N in low-level eutrophication water.In medium to high-level eutrophication water,1 and 10μM SNP could enhance the absorption rate and the demand amount for N（the amount of N absorbed from the water per unit weight of water hyacinth）,the difference was that in medium-level eutrophication water,SNP mainly promoted the root growth of water hyacinth,while the amount of N required for water hyacinth growth was the same for 1μM and 10μM SNP groups.However,in high-level eutrophication water,SNP stimulated branching of water hyacinth,and the demand for N was highest in 10μM SNP group.SNP with concentrations higher than 50μM caused an increase in TN in all three-level eutrophication and inhibited the growth of water hyacinth.Compared to the single treatment group of water hyacinth group,SNP with concentrations lower than 10μM had no effect on the P uptake of by water hyacinth in low,medium and high-level eutrophication water.SNP with concentrations equal to or higher than50μM caused a rapid decrease in P content in water,accompaning by precipitation formation.Therefore,10μM was chosen as a dosage of SNP promote water hyacinth’s absorption of TN from water and increase its nitrogen requirement for growth.a dosage of（2）The effect mechanism of SNP on the absorption of N and the growth and development of water hyacinth from the perspective of N assimilation.Compared to the control group,in low-level eutrophication water,the activities of nitrate reductase（NR）,glutamate oxaloacetate transaminase（GOT）,and glutamic-pyruvic transaminase（GPT）increased,and the content of nitrate nitrogen（NO₃^-）and free amino acids（FAA）increased in water hyacinth roots after treatment with 1μM SNP.Treatment with 10μM SNP had no effect on these indices,while treatment with 50μM SNP caused a decrease in the activities of NR,nitrite reductase,GOT,and GPT in water hyacinth roots,and a decrease in the contents of NO₃^-,ammonium nitrogen（NH₄⁺）,and FAA.In medium-level eutrophication water,treatment with 1and 10μM SNP both led to an increase in the activities of NR,nitrite reductase,glutamine synthetase,GOT,and GPT,and an increase in the contents of NO₃^-,NH₄⁺,and FAA in water hyacinth roots.Treatment with 50μM SNP caused a decrease in the activities of glutamine synthetase and glutamate synthase compared to the low-level eutrophication water.In high-level eutrophication water,the effects of SNP on the N assimilation in water hyacinth roots were similar to those in medium-level eutrophication water.Therefore,SNP affects the growth and development of water hyacinth and the absorption of TN in water by regulating the activities of key enzymes and the contents of key products of N assimilation in water hyacinth roots.（3）From the perspective of SNP decomposition products,the effect mechanism of SNP on root N assimilation and the growth development of water hyacinth was revealed.First,the concentrations of the final SNP decomposition products,i.e.NO,NO₂^-,CN^-and Fe（CN）₆^4-were determined.Then,Na NO₂ and K?Fe（CN）?were separately applied to water hyacinth at the same concentration to simulate the effects of NO₂^-,CN^-and Fe（CN）₆^4-on water hyacinth,and NO scavenger carboxy-PTIO potassium salt（c PTIO）was used to determine the effects of NO on water hyacinth.The results showed that compared with the single treatment with water hyacinth,Na NO₂ and K?Fe（CN）?treatment had no effect on N assimilation as well as the growth and development of water hyacinth;single c PTIO treatment inhibited the N assimilation as well as the growth and development of water hyacinth roots,while single SNP treatment promoted N assimilation as well as the growth and development of water hyacinth roots,and the combined treatment of c PTIO and SNP had no effect on N assimilation as well as the growth and development of water hyacinth roots.Therefore,it was determined that the effects of SNP on N assimilation as well as thegrowth and development of water hyacinth were realized by the NO produced by SNP decomposition.In summary,SNP with concentrations of lower than 10μM enhances the activity of enzymes and the contents of key products of N assimilation in water hyacinth roots through NO produced by its decomposition.Its manifestation varies with the degree of eutrophication of the water body,i.e.,promoting rooting in low and moderate-level eutrophication water,and promoting branching in high-level eutrophication water.As the growth of roots and branches increases the demand for N,the absorption rate of N by water hyacinth and the required amount of N for growth increase.