The Role Of Nitrogen And Phosphorus On Salix Viminalis In Response To Cadmium

In recent years,the continuous development of cities and industries in our country has caused the serious soil Cd²⁺pollution,Cd²⁺will harm people’s health through the food chain,so it is of great significance to study the measures to repair the soil polluted by Cd²⁺.Proper application of fertilizer can alleviate the toxic effect of heavy metals on plants and enhance their resistance.In this study,the effects of different concentrations of nitrogen and phosphorus on photosynthesis,membrane lipid peroxidation and osmotic adjustment of Salix viminalis under cadmium stress were investigated,the optimum combination of nitrogen and phosphorus was obtained to enhance the cadmium resistance of Salix viminalis.Then study the difference of resistance of nitrogen,phosphorus and their interaction to Salix viminalis under cadmium stress,and the differences of cadmium transport,accumulation and distribution in each organ of Salix viminalis.The mechanism of increasing tolerance of nitrogen and phosphorus to heavy metal cadmium in Salix viminalis was studied from physiological and molecular aspects.This study will be helpful to improve the application value of Salix viminalis in remediation of heavy metal contaminated soil,and provide theoretical and practical significance for further research on mineral elements promoting phytoremediation of heavy metal contaminated soil.The results were as follows:（1）After adding different concentrations of nitrogen and phosphorus to Salix viminalis under Cd²⁺stress,the interaction of nitrogen and phosphorus was found to promote plant growth and development,increase plant biomass,improve plant physiological status and enhance plant resistance to adversity.The results showed that adding 3.73mmol·L^-1NH₄Cl and0.6mmol·L^-1Na H₂PO₄·2H₂O could enhance the resistance of Salix viminalis to cadmium stress.（2）The effects of N,P and their interaction on MDA content in leaves and roots of Salix viminalis under Cd²⁺stress are significant different.The effect of Cd+N+P treatment on resistance of Salix viminalis leaves is better than that Cd+N and Cd+P.The MDA content of Salix viminalis root under cadmium stress is significantly lower than that under cadmium stress,especially under Cd+N and Cd+N+P.Under cadmium stress,the content of hydrogen peroxide in leaves is significantly higher than that in roots,and Cd+P treatment have the most significant effect on reducing the content of hydrogen peroxide in leaves,while Cd+N and Cd+P treatment have the most obvious effect on reducing the content of hydrogen peroxide in roots.（3）The effects of N,P and their interactions on antioxidant enzyme activity of Salix viminalis leaves and root under cadmium stress showed that the Cd+N+P treatment have the most obvious enhancement effect on SOD activity.Secondly,Cd+N treatment enhance SOD activity in root better than Cd+P treatment,while Cd+P treatment have a significant effect on SOD activity in leaves than Cd+N treatment;the activities of POD in leaves of Salix viminalis under Cd+N+P stress are the most obvious,the activities of POD in roots of Salix viminalis under Cd+N stress are the most obvious;Cd+N treatment significantly increase glutathione reductase activity in leaves of Salix viminalis,while Cd+N+P treatment significantly increase glutathione reductase activity in roots of Salix viminalis.The Cd+P treatment is the most significant way to increase APX activity in leaves of Salix viminalis,while the Cd+N treatment is the most significant way to increase APX activity in roots of Salix viminalis.（4）The effects of N,P and their interactions on the osmotic regulators in leaves and roots of Salix viminalis under cadmium stress were shown as follows:the application of nitrogen and phosphorus under cadmium stress could reduce the soluble protein content of Salix viminalis,and the Cd+N treatment have the most obvious effect.Cd+P treatment reduce the content of free proline in leaves of Salix viminalis and Cd+N treatment reduce the content of free proline in roots of Salix viminalis.Under cadmium stress,there was no significant difference in the soluble sugar content of Salix viminalis under nitrogen and phosphorus treatment,Cd+P treatment have the most significant effect on the soluble sugar content of the leaves of Salix viminalis,and Cd+N treatment had a significant effect on the soluble sugar content of the roots of artemisia willows.（5）Under cadmium stress,the application of nitrogen and phosphorus treatment significantly affected the cadmium content in the root system and overground part of Salix viminalis.Cd+P treatment significantly increase the cadmium content in the root system of Salix viminalis.Cd+N treatment significantly increase the cadmium content in the overground part of Salix viminalis.The application of nitrogen and phosphorus have a significant effect on the heavy metal cadmium transport of Salix viminalis.The Cd+N treatment could significantly promote the transport of cadmium from roots to leaves and increase the cadmium transport coefficient of Salix viminalis.The Cd+P treatment could significantly inhibit the transport of cadmium from roots to leaves and reduce the cadmium transport coefficient of Salix viminalis.（6）Under cadmium stress,N and P treatments significantly increase the expression of heavy metal detoxification and transport related genes in the roots of Salix viminalis,in which the Cd+N+P treatment significantly increase the expression of heavy metal detoxification related genes,and the Cd+N treatment significantly increase the expression of heavy metal transportation-related genes.To sum up,applying N and P under Cd²⁺stress can enhance the resistance of Salix viminalis to cadmium,and change the accumulation and transport characteristics of Cd²⁺,The effect of nitrogen and phosphorus interaction on cadmium resistance of Salix viminalis is little different from that of single application of nitrogen and phosphorus.The interaction of nitrogen and phosphorus significantly reduce the membrane lipid peroxidation of Salix viminalis,increase the expression of heavy metal detoxification related genes,and increase the resistance of Salix viminalis to cadmium.Nitrogen application significantly increase the activity of antioxidant enzymes in the roots of Salix viminalis,decrease the osmotic adjustment substances in Salix viminalis,and decrease the stress of cadmium on the roots of Salix viminalis.At the same time,nitrogen treatment significantly promote the transfer of cadmium from roots to leaves,increase the cadmium transfer coefficient of Salix viminalis,and the expression of heavy metal transfer related genes are also significantly increase.The resistance of Salix viminalis to cadmium was increased by applying phosphorus under cadmium stress,decreasing the transfer Coefficient of cadmium in Salix viminalis.