Study On The Effect Of Nitrogen Nutrition On Soybean Nodulation And Nitrogen Fixation And Related Regulation Substances

As an important grain and oil crop in China,Soybean is a valuable biological resource with rich nutritional value,strong physiological activity and wide range of applications.Nitrogen,as an essential element of soybean,affects the growth and development of soybean in all aspects.The relationship between nitrogen and root nodule nitrogen fixation is a combination of cooperation and contradiction.When nitrogen is combined with nodules nitrogen fixation,it can reach high yield,but the contradiction between the two will have an adverse effect on nodules nitrogen fixation,and The reason why nitrogen affects root nodulation mechanism remains unclear.The experiment was carried out at the University of Northeast Agricultural University's experimental base in 2015-2017.The experiment used the double root system of grafted soybeans to apply nitrogen locally to the soybean root,set a plurality of nitrogen concentration gradients,and perform nitrogen concentration changes.Further study on the regulatory relationship between nitrogen nutrition and soybean nodulation and nitrogen fixation,at the same time,testing and analysis of possible regulatory substances associated with it.The ¹⁵N method was used to determine the rate of nitrogen fixation in root nodules,and the differences in nitrogen fixation ability of soybean varieties at different growth stages under different nitrogen concentrations were explored.The results showed that:In the dual root systems constructed by seedling grafting,the number and weight of root nodules at the N+side both exhibited a single-peak changing trend of first increasing and then decreasing with nitrogen concentrations.Root nodulation was accelerated by low concentrations of nitrogen?<50 mg/L?and significantly suppressed by high concentrations of nitrogen?>50mg/L?.In contrast,the number and weight of root nodules at the?N-?side showed a constant increasing trend with the increase in nitrogen concentrations.And at high nitrogen levels?above50 mg/L?,the number and weight of nitrogen-applied?N+?root nodules was significantly lower than that of the non-nitrogen-applied side?N-?.These results indicated that high nitrogen concentration exerts a contact-dependent localized inhibitory effect on the formation?number of nodules?and growth of root nodules?weight of nodules?.In the double root system of soybean,The nitrogenase activities in the root nodules at both the?N+?and the?N-?sides displayed trends of first increasing and then decreasing with nitrogen concentrations,reaching a single peak when the nitrogen concentration was 50 mg/L.In addition,the promotive or inhibitory effects of nitrogen at different concentrations on nitrogenase activity in the root nodules were synchronous between the?N+?and the?N-?sides,suggesting that the effect of nitrogen is systematically regulated via interactions between the aboveground and underground parts of the plants.In the double root system of soybean,when nitrogen was applied to one side of the root?100mg/L?,the free aspartic acid content in the phloem of the nitrogen application?N+?increased significantly after nitrogen treatment,and decreased after nitrogen application was stopped.The content of free aspartic acid on the unfertilized side?N-?was not significantly affected,The free glutamic acid content did not show the same apparent effect as aspartic acid,suggesting that nitrogen may increase phloem aspartic The content of amino acids regulates soybean nodulation and nitrogen fixation.In the double root system of soybean,nitrogen?100 mg/L?was applied locally to one side root,the daidzin,daidzein,genistin,genistein,glycitein and total isoflavone content in the nitrogen?N+?and non-nitrogen?N-?roots were increased significantly and decreased after nitrogen application was stopped.This indicates that the content of isoflavones in soybean roots is systematically regulated by nitrogen.In the double root system of soybean,the treatment of nitrogen?100 mg/L?on one side of the roots had significant effects on the root-related hormone content.The content of jasmonic acid and indole acetic acid did not change significantly,but the content of gibberellin in the nitrogen-applied?N+?and non-nitrogen-applied?N-?roots increased after nitrogen application,and decreased after nitrogen application was stopped.The nitrogen?N+?salicylic acid content decreased significantly after nitrogen treatment and was restored after the nitrogen application was stopped.The nitrogen-side?N-?salicylic acid content was less affected,indicating that the gibberellin and the soybean root system contained gibberellin and Salicylic acid content may be related to nitrogen inhibition of nodulation and nitrogen fixation.In the double root system of soybean,nitrogen is applied to one side of the root,and the higher nitrogen supply concentration?above 50 mg/L?can significantly promote the growth and development of the shoot and both sides of the roots.The larger the concentration was,the more obvious the promotion effect was.Although nitrogen application promoted dry matter accumulation in the non-nitrogen-applied?N-?roots,the growth of nitrogen-applied?N+?roots was significantly greater than that of non-nitrogen-applied?N-?roots,especially at high nitrogen concentrations,especially at high nitrogen concentrations,The results showed that the soybean root system showed nitrogen-promoting effect on high concentration of nitrogen;And the change of nitrogen concentration on the nitrogen application side?N+?can significantly change the C/N in the shoots and the roots of nitrogen-applied?N+?.The higher the nitrogen concentration,the lower the C/N of the shoot and nitrogen-applied?N+?roots.For the 4 soybean varieties tested?2 early-maturing and 2 late-maturing varieties?,¹⁵N-labeled ammonium sulfate was applied at different concentrations.During the three sampling periods of R₁,R₅,and R₈,nodule nitrogen fixation rates of the four soybean varieties decreased significantly with the increase of N concentration,and there was no significant difference in nitrogen fixation rate among the varieties,This indicated that the nitrogen fixation rate of the early-maturing varieties and late-maturing varieties had no significant difference,but was only affected by the nitrogen concentration,And with the increase of nitrogen levels,soybean production increased significantly.