Culture Condition Optimization Of A Nitrate-degrading Strain ZJS And Its Application To Alleviate Nitrate Stress In Cucumber

Cucumber,as an important cash crop,is easily subjected to nitrate stress due to the secondary salinization of soil in its growing environment,which seriously affects the quality and yield of cucumber.In this experiment,KNO3 was added to the soil to simulate nitrate stress,and then bacterial agent made from ZJS strain was applied to the soil to study its mitigation effect on nitrate stress in cucumber seedlings.Specific research contents and results are as follows:In this study,a strain ZJS with the ability to degrade nitrate was isolated from rhizosphere soil of plants for molecular identification,and the strain was identified as Pseudomonas sp.By optimizing the culture conditions,the optimal culture temperature of ZJS was 37,the medium p H was 7,the concentration of KH2PO4 was 5g/L,the carbon source was glucose,and the nitrogen source was ammonium nitrate.Under this condition,the number of viable bacteria was（3.07±0.018）10 ⁸cfu/m L when ZJS was cultured for 12h.The indoleacetic acid（IAA）production capacity of ZJS,the activity of1-aminocyclopropane-1-carboxylic acid deaminase（ACC deaminase）and the content of extracellular polysaccharide were determined.The results showed that ZJS could produce up to 18.548 0.163 g/m L of IAA,the highest ACC deaminase activity was 0.638±0.012 mol peg-ketobutyric acid mg^-1h^-1Pr,and the maximum extracellular polysaccharide content was8.37±0.146 g/m L.The results of potted experiment showed that,after 12 days of cultivating cucumber seedlings,the cucumber plant height,leaf area,dry weight,fresh weight and water content of leaves in KNO3 group all decreased significantly compared with the control group.The content of Malondialdehyde（MDA）and H2O2 in leaves increased by 65.07%and 8.4%,respectively.The contents of soluble sugar proline and soluble protein in leaves increased by24.07%,50.7%and 112.23,respectively.The activity of antioxidant enzymes APX,SOD,CAT,and DHAR in leaves decreased by 37.93%,25.01%,38.46%,and 31.25%,respectively.The content of antioxidant As A and GSH in leav es decreased by 36.36%and 27.59%respectively.Compared with that in the ZJS+KNO3 group and the KNO3 group,the dry fresh weight and relative water content of the above-ground part of the plant height and leaf area increased significantly.The content of MDA and H2O2 in leaves decreased by 19.4%and16.65,respectively.The contents of proline and soluble protein decreased by 31.76%and28.81%respectively,while the contents of soluble sugar decreased but not significantly.The activity of antioxidant enzymes APX,SOD,CAT,and DHAR in leaves increased by 61.43%,40.01%,42.86%and 45%,respectively.The content of antioxidant As A and GSH in leaves increased by 92.86%and 76.19%,respectively.The results showed that the soil phosphatase catalase urease and sucrase activities in KNO3 group decreased by 37.73%,31.25%,27.78%and 29.41%,respectively,compared with the control group.Compared with the KNO3 group,the activity of soil phosphatase,catalase,urease,and sucrase in ZJS+KNO3 group increased by 107.88%,45.45%,69.23%,and 60.42%,respectively.The activities of urease phosphatase and sucrase in soil of ZJS group were increased compared with that of the control group.Comprehensive the above experimental results show that nitrate stress seriously hindered the growth of cucumber,and exert ZJS can to a certain extent,improve the growth of the cucumber,alleviate nitrate stress at the same time promote the growth of cucumber for nitrate degradation bacteria helps relieve the stress of crops of cucumber nitrate and the researches on the mechanism of the new type microbial agents improved nitrate stress and provide theoretical basis for the development and utilization of effective strain,have good practical significance.