Study On Nitrogen Efficiency Mechanism And Division Growth Period By Nitrogen Nutrition Stage Of Alfalfa

Nitrogen application is an important measure to improve alfalfa yield.Low nitrogen use efficiency rate cannot only reduce both industry and ecological but also affect the sustainable development in agricultural.Therefore,it is the fundamental way to improve the nitrogen use efficiency by the biological way to dig alfalfa efficient absorption and utilization of nitrogen nutrition potential.In this study,a variety of origin within the country,with a typical representative alfalfa varieties were used as test materials to establish the evaluation system of alfalfa nitrogen efficienty under seeding screening and full growth period and field area validation.Further,different nitrogen efficienty type varieties were used,to analyze difference of root morphological and physiological characteristics,nitrogen metabolism key enzyme activity,photosynthetic physiological traits,nodulation and nitrogen fixation characteristics,transmission tissue anatomical structure and gene expression characteristics.The growth period of alfalfa was dominated by nitrogen nutrition stage,through the vegetative growth period and whole growth period.The main results were as follows: 1.The evaluation system of alfalfa nitrogen efficienty was establishedThe performance of the screened different N-efficient genotypes at the growth period and each time cutting were consistent with that of seedling stage,the evaluation system of alfalfa nitrogen efficienty was established.The data was analyzed by indexes variation and correlation analysis,shoot and plant dry weight,root length,root volume,shoot and plant nitrogen accumulation were the indexes.They were divied into four nitrogen efficiency types by membership function method and cluster analysis,?1?double-efficiency which had high NUE in low N and normal N;?2?high efficiency in high-N which had high NUE in normal N and low NUE in low N;?3?high efficiency in low-N which had low NUE in normal N and high NUE in low N;?4?double-inefficiency which had low NUE in low N and normal N.6010 being the double-efficiency,Gannong No.3 being high efficiency in high-N,Gannong No.7 being high efficiency in low-N,Longdong being the double-inefficiency type.The uptake and utilization efficiency,yield and quality of double-efficiency were higher than that of double-inefficiency.Comprehensive data,double higher in the economic benefits of more applicable.2.Differences in nitrogen efficient mechanism of alfalfa2.1 Under low-N stress,the root morphology and root volume were higher than normal-N from seedling to budding period,after the budding period is the opposite.There was no obvious difference between root morphological and root physiological index.The total root length and root volume of double-efficiency were higher than double-inefficiency,but also had strong root activity,more developed root system,stronger ability of N absorption,higher accumulation and utilization.It can be seen that root size and vigor were the underlying causes of nitrogen efficiency differences.2.2 The changes of nodule number,nodule weight and nitrogen fixation ability of different nitrogen efficiency types were the same,showing a single peak curve,and the maximum in podding period.They were increased with nitrogen concentration increased.The nitrogen fixation ability of double efficiency and high efficiency in low N were strengthened under low-N,double efficiency and high efficiency in high N were strengthened under normal-N.2.3 There were significant genotypic differences in NR,GS,GOGAT,GDH,GOT and GPT activities in alfalfa,with the growth period showed a single peak curve changes and peak in the flowering period.The activities of NR and GS were the highest in the double efficient varieties and the lowest in the double inefficiency,the other two categories were in the middle.This is consistent with the metabolic characteristics of nitrogen nutrition types,so NR and GS activity can be used as an indicator of nitrogen efficiency evaluation.2.4 There were significant genotypic differences in photosynthetic effect parameters.Chlorophyll content,photosynthetic rate,stomatic conductance and transpiration rate of double efficient varieties were higher than double inefficiency,consistent with the changes in dry matter production,CO₂ concentration was the opposite.When the nitrogen level was increased,the photosynthetic rate of double-efficiency was the largest,and the increase rate of photosynthetic rate was the largest in high nitrogen,and the smallest in the high efficiency in low N,the other two categories were in the middle.2.5 Related index of anatomical structure of the guided tissue in normal-N were higher than low-N.Transport orgarization of double efficiency and low nitrogen were more developed under low-N,double efficiency and high nitrogen in low N were more developed under normal-N.Double efficient transport tissue development is best,double inefficient type of the worst,the other two between the middle.3.Differences in gene expression characteristicsHigher expression of AMT and NRT2 were observed in the root of double-efficient.Higher expression of NRT2 was observed in the shoot of double-efficient.It has a strong ability to absorb and transport AMT and NRT.4.resource of nitrogen of alfalfa growth period4.1 During vegetative growth,under low-N,the alfalfa plant depened maily on fertilizer N to 50 d,the two nitrogen sources were flat in 60 d,depened maily on nodules N in 70 d.Under normal-N,the alfalfa plant depened maily on fertilizer N in vegetative period.Fertilizer N and nodule N accumulation mainly in aerial part,the proportion that aerial part occupied 64.8% and 53.6% in low N,occupied 71.6% and 72.4% in normal N.4.2 Nitrogen nutrition of alfalfa may be divided into three stages: From the first trifoliolate stage to beginning bloom,where the plant absorbs mainly soil-N and fertilizer-N.Effect of nitrogen fixation in 6010 was higher than in Longdong,and the proportion of soil nitrogen was less than in Longdong.From the early flowering to the full pod,where the plant absorbs mainly soli-N,fertilizer-N and nodule-N.The proportion of soil-N absorbed by two cultivars was close,fertilizer-N and noudle-N absorbed were different,fertilizer-N 21.1% in Longdong,9.6% in 6010.From drum to full maturity stage,where the nitrogen comes mainly from the nitrogen fixation by nodules,the contribution of nodule-N was 88.4%⁸9.6%,soil-N was 4.1%¹0.0% and fertilizer-N was 1.5%⁶.4%.