Study On The Characteristics And Regulation Mechanism Of Nitrogen Efficiency Of Alfalfa

With the vigorous development of China animal husbandry,As a high-quality protein forage,alfalfa(Medicago sativa)has become increasingly important.However,alfalfa varieties are diverse,and their response to nitrogen is also different.Nitrogen-efficient alfalfa can achieve the effects of low fertilizer and high yield,resource conservation,and environmental protection.Therefore,in order to explore the regulation mechanism of alfalfa nitrogen efficiency,this study selected 8 alfalfa varieties as representatives based on the team’s previous research results on alfalfa nitrogen utilization.Through the study of their nitrogen absorption,fixation and nitrogen transformation capabilities,Screening of nitrogen-efficient alfalfa varieties and discussing the main factors affecting the difference in nitrogen efficiency of alfalfa.At the same time,this study also studied the correlation between four isoflavones of luteolin,genistein,daidzein and formononetin and the nodulation and nitrogen fixation of alfalfa with different nitrogen efficiency,as well as the expression of isoflavone synthase(IFS)and tumor signaling pathway(nod)related genes.The results of the research are as follows:1.The difference in nitrogen efficiency of alfalfa and its influencing factorsThe difference in nitrogen efficiency of alfalfa: The growth characteristics,nitrogen fixation characteristics,nitrogen absorption characteristics and nitrogen transformation ability of alfalfa all have certain differences among varieties.The coefficients of variation of the comprehensive values of the nitrogen efficiency membership functions of the eight alfalfa varieties selected in this study under low nitrogen,suitable nitrogen,and high nitrogen treatments reached 54.66%,49.44%,and 43.22%,respectively.Among the varieties,"Gannong No.5" had the highest nitrogen efficiency,followed by "LW6010",and its average nitrogen efficiency membership function comprehensive value reached 0.671 and 0.665,respectively."Gannong No.5" and "LW6010" alfalfa can use their own characteristics to achieve high yield in both low nitrogen and high nitrogen environments.Division of nitrogen efficiency types of alfalfa: The 8 alfalfa varieties tested are divided into 4 different nitrogen efficiency types through cluster analysis and the comprehensive value of nitrogen efficiency membership function: "LW6010" and "Gannong No.5" both have a higher comprehensive value of nitrogen efficiency under different nitrogen levels,which is classified as nitrogen efficient type;"Gannong No.3" and "Xinmu No.1" have lower comprehensive values of nitrogen efficiency under low nitrogen,but with the increase of the level of nitrogen,the comprehensive value of nitrogen efficiency showing a trend of rising first and then falling,so it is classified as normal-effect type;"Gannong No.7" and "Longmu 801" have higher comprehensive value of nitrogen efficiency under low nitrogen level,but with the nitrogen level increases,the comprehensive nitrogen efficiency value also decreases,so it is classified as an inverse type;the comprehensive nitrogen efficiency values of "LD Alfalfa" and "Golden Queen" are lower at different nitrogen levels,so they divided into inefficient type.Influencing factors of alfalfa nitrogen efficiency: Weighting 21 indicators related to alfalfa nitrogen efficiency through principal component analysis,and normalizing the weights to obtain the specific contribution rate of each influencing factor to alfalfa nitrogen efficiency.For alfalfa,the nitrogen conversion capacity has the largest contribution rate to its nitrogen efficiency,followed by the nitrogen fixation characteristics;among the influencing factors,the number of nodules and nodule weight of alfalfa are the decisive factors affecting its nitrogen efficiency.The contribution rate of nitrogen efficiency reached 9.49% and 9.47%,ranking first and second.2.Regulation of isoflavones on nitrogen efficiency of alfalfaThe nodulation,nitrogen fixation and isoflavone content of alfalfa: The nodulation,nitrogen fixation and isoflavone content of alfalfa are significantly positively correlated.When the concentration of exogenous nitrogen changes,alfalfa can increase luteolin,genistein,daidzein,formononetin and total isoflavone content in the stems,leaves and roots.Thereby promoting nodulation to increase the nitrogen fixation potential of a single plant.Regulation of isoflavones on nodulation and nitrogen fixation of alfalfa with different nitrogen efficiency: The regulation of isoflavones on nodulation and nitrogen fixation of alfalfa differs among varieties with different nitrogen efficiency.Nitrogen-efficient alfalfa promotes nodulation and nitrogen fixation by synergistic upregulation of IFS genes expression to increase isoflavone content under nitrogen stress.Nitrogen-low-efficiency alfalfa has only part of the IFS genes up-regulated under nitrogen stress,so its nodulation and nitrogen fixation ability is low.The regulation mechanism of isoflavones on the nitrogen efficiency of alfalfa:Alfalfa mainly synthesizes isoflavones through the expression of IFS gene in stems and leaves and IFS-1,IFS-2 genes in roots,and then stimulates the expression of nod-1,nod-2 genes in stems and leaves and nod-1 gene in roots to promotes nodulation and nitrogen fixation,thereby regulating the nitrogen efficiency of alfalfa.Nitrogen-efficient alfalfa is because the high expression of IFS genes under nitrogen stress synthesizes more isoflavones,which in turn stimulates the high expression of nod genes to promote nodulation and nitrogen fixation,thereby improving nitrogen efficiency.As a result,the nitrogen efficiency of alfalfa can be improved by manipulating the expression of IFS genes in the isoflavone synthesis pathway,thus improving its agronomic characters and increasing economic benefits.