Study On The Difference Of Genotypic Characteristics And Physiological Mechanism Of Different Nitrogen Efficiency In Wheat

Wheat is one of the most important food crops in the world,and the application of nitrogen fertilizer plays an important role in improving the yield of wheat.However,for a long time,there has been the problem of excessive application of nitrogen fertilizer and low nitrogen use efficiency in wheat production in many countries,and the excessive application of nitrogen fertilizer also causes non-point source pollution.Therefore,the study on the morphological and physiological characteristics of wheat varieties with different nitrogen use efficiency under different nitrogen levels will be beneficial to the genetic improvement of fertilizer-saving and high-yield varieties.In this study,three wheat varieties Zhoumai 32,Zhengmai 1860,Zhengmai 7698 and three wheat varieties R93127,Yumai 61 and Xiaoyan 6 with low nitrogen use efficiency were used as experimental materials.The water culture experiment was conducted in a light incubator to analyze the differences of root morphological characteristics(root tip number,root length,root diameter,root volume and root surface area),root activity and six nitrate transport protein related genes(Ta NRT2.1,Ta NRT2.2,Ta NRT2.3,Ta NAR2.1,Ta NAR2.2 and Ta NAR2.3)of wheat varieties with different nitrogen efficiency at seedling stage.The field experiment was carried out in the Modern Agricultural Research and Development Base of Henan Academy of Agricultural Sciences from 2019 to 2021.The soil type of the experiment was light loam.The experiment was divided into two treatment areas:high nitrogen(HN)and low nitrogen(LN).The differences of aboveground nitrogen accumulation,chlorophyll relative content,plant height,key enzymes of nitrogen assimilation(nitrate reductase,glutamine synthetase,glutamate synthetase,glutamate dehydrogenase)of wheat varieties with different nitrogen efficiency at different stages,the contribution rate of plant pre-anthesis nitrogen transport,plant post-anthesis nitrogen uptake and pre-anthesis nitrogen transport to grain nitrogen accumulation,The contribution of nitrogen uptake after anthesis to grain nitrogen accumulation,the difference of nitrogen distribution ratio in different parts of plant at flowering stage and the difference of nitrogen distribution ratio in different parts of plant at mature stage were compared.The main results are as follows:1.The main root morphological characteristics,root activity and nitrate transporter gene expression of nitrogen efficient varieties were significantly better than those of nitrogen inefficient varieties,showing higher nitrogen absorption capacity.Under high nitrogen environment and low nitrogen environment,the root tip number,root length,root volume,root surface area and root activity of nitrogen efficient varieties were significantly higher than those of nitrogen inefficient varieties.especially under the condition of low nitrogen,the root length,root volume,root surface area,root tip number and root activity were 19.5%,112.2%,87.05%,109.9%and 155.7% more than those of nitrogen inefficient varieties,respectively.Under the condition of low nitrogen,the average relative expression of six nitrate transporter genes in nitrogen efficient varieties was 1.93 times,2.3 times,2.13 times,2.27 times,2.00 times and 3.17 times higher than that in nitrogen inefficient varieties,respectively.this showed that the gene upregulation ability of nitrogen efficient varieties was significantly higher than that of nitrogen inefficient varieties.Therefore,nitrogen efficient varieties still have strong ability of nitrogen absorption and transport in low nitrogen environment.2.The nitrogen assimilation enzyme activity of nitrogen efficient varieties was significantly higher than that of nitrogen inefficient varieties,showing higher nitrogen assimilation ability.The activities of nitrate reductase(NR),glutamine synthetase(GS),glutamate synthase(GOGAT)and glutamate dehydrogenase(GDH)in nitrogen efficient varieties were significantly higher than those in nitrogen inefficient varieties at full heading stage,flowering stage and 15 days after anthesis.After low nitrogen treatment,the nitrate reductase activity of nitrogen efficient varieties decreased by3.2%-9.3%,glutamine synthetase activity decreased by 4.5%-16.5%,glutamate synthetase activity decreased by 4.7%-11.9%,and glutamate dehydrogenase activity decreased by more than 3.0%.This shows that the activities of the four nitrogen metabolism related enzymes of nitrogen efficient varieties are more stable than those of nitrogen inefficient varieties,and their changes are relatively less affected by low nitrogen,which also shows that nitrogen efficient varieties have stronger ability of nitrogen assimilation under the same conditions.3.The ability of pre-anthesis nitrogen accumulation and utilization of nitrogen efficient varieties was significantly better than that of nitrogen inefficient varieties,showing the characteristics of higher nitrogen accumulation,free amino acid content and relative chlorophyll content,and small variation of plant height under different nitrogen conditions.Under the environment of high and low nitrogen,the nitrogen accumulation of nitrogen efficient varieties was significantly higher than that of nitrogen inefficient varieties at jointing stage,booting stage and flowering stage.After low nitrogen treatment,the nitrogen accumulation of nitrogen efficient varieties at jointing stage,booting stage and flowering stage decreased by 7.6%-11.8%,chlorophyll relative content decreased by 7.1%-12.2%,plant height decreased by4.4%-12.2%,and free amino acid content decreased by 5.0%-25.7%.This shows that the decrease of nitrogen level has little effect on nitrogen accumulation,chlorophyll relative content,plant height and free amino acid content of nitrogen efficient varieties,indicating that nitrogen efficient varieties can effectively utilize available nitrogen resources to meet the needs of their own growth and development.4.The nitrogen absorption capacity and translocation ability of nitrogen efficient varieties were significantly higher than those of nitrogen inefficient varieties at grain filling stage,and finally showed higher nitrogen use efficiency.The post-anthesis nitrogen uptake of nitrogen efficient varieties under high nitrogen and low nitrogen conditions was 100% and 18.6% more than that of nitrogen inefficient varieties,respectively.At flowering stage,the proportion of stem and sheath of nitrogen efficient varieties was higher than that of nitrogen inefficient varieties at flowering stage,and the stem and sheath proportion of nitrogen efficient varieties was higher than that of nitrogen inefficient varieties at maturity.This shows that nitrogen efficient varieties can not only show the characteristics of high nitrogen absorption after anthesis under the condition of high nitrogen,but also have outstanding high nitrogen absorption capacity after anthesis under the condition of low nitrogen,which provides the necessary conditions for high-speed and efficient nitrogen transport in the later stage.