| Green onion is a vegetable in our daily life.The value of nutritional is very large,and the economic benefits brought cannot be ignored.In order to improve the yield and quality of green onions,people have done a lot of research about the fertilization program of green onions.As nitrogen seen as an important nutrient element,nitrogen can not only promote plant growth and increase yield,but also increase its quality.In order to explore the effects of nitrogen levels on the growth quality of green onions,this topic uses urea as a nitrogen source.The experiment plant is Jinan Zhangqiu green onion.As experimental materials,the test field was divided into several micro-areas in Jinan Zhangqiu experimental field,and different levels of urea were applied to the micro-areas,including nitrogen-free fertilizer（0 kg/ha）,total nitrogen fertilizer（260kg/ha）and nitrogen fertilizer halved（130 kg/ha）.The other conditions are the same.in the summer season of the green onion（July 17）,the fast-growing period of the leaf cluster（September 11）,the period of the full stem filling（October 20）,and the harvest period（November 13）Sampling,5-10 strains of green onions were randomly selected for each treatment to tests the growth quality,trace element content,enzyme activity related of nitrogen metabolism,rhizosphere soil flora structure and the effect of gene expression.The main findings are as follows:1.After treatment with different nitrogen levels,the fresh weight and dry weight of the stems and leaves of the green onion increased with the increase of nitrogen fertilizer content,and the effect was very significant.With the treatment of nitrogen fertilizer halving and total nitrogen fertilizer,the weight of the fresh stalks increased39.1%and 56.9%respectively,and the dry weight of pseudostem increase 33.7%and48.6%,respectively.In terms of leaves,the fresh weight of green onion treated with nitrogen fertilizer increased by 38.2%and 93.4%compared with nitrogen-free fertilizer treatment.The increase was 56.7%and 111.3%in weight of leaves dried,respectively.In addition,Nitrogen also promoted plant height and root growth.But nitrogen had little effect on the pseudo-stem length of green onion.This shows that nitrogen fertilizer can significantly increase the yield and quality of green onions.2.Trace elements play a huge role in the growth and development of the human body,especially in the formation of some enzymes and hormones.The green onions contain a lot of trace elements.In order to understand the effect of nitrogen on the trace elements of green onions,we use nitric acid and 27%H2O2 to decomposed it and its trace element content was determined by inductively coupled ICP-MS.The results showed that the total amount of trace elements in green onion decreased with the increase of nitrogen level.The content of trace elements treated with nitrogen fertilizer reduced by 47.83%,and the content of Mn,Fe,Cu and Zn was also gradually reduced with the increase of nitrogen levels.Under the influence,the trace elements content of leaves decreased gradually in Mn,Cu and Zn,while the content of Fe increased rapidly.In the scallio,the content of Fe,Cu and Zn decreased gradually with the increase of nitrogen level.The content of Ca and Mn increased first and then decreased.In terms of pseudo-stem quality,the content of free amino acid,soluble protein,pyruvic acid and nitrate in green onion increased with the increase of nitrogen level,and soluble sugar and vitamin C showed a trend of increasing first and then decreasing.3.In plants,nitrogen metabolism is inseparable from the participation of a series of related enzymes.There are four enzymes related to nitrogen metabolism including nitrogen reductase（NR）,glutamine synthetase（GS）,glutamate synthase（GOGAT）,glutamate dehydrogenase（GDH）.Nitrate reductase showed a trend of increasing first and then decreasing with the increase of nitrogen content.The enzyme was affected by nitrogen in the fast stage of leaf plexus,which was larger than other periods.When the nitrogen fertilizer was halved,the enzyme was affected and increased by 79.9%.Under the influence of nitrogen,the activity of glutamine synthetase was higher than that under the condition of no nitrogen fertilizer.With the increase of nitrogen levels,the activity of glutamate synthetase increased first and then decreased.Nitrogen had the greatest effect on the enzyme in the stage of the leaf plexus and the period of pseudo-stem filling.The glutamate dehydrogenase had the highest enzyme activity under the treatment of nitrogen fertilizer halving.The result of nitrogen fertilizer halving level is superior to the other two conditions.4.Nitrogen is an important nutrient element for plant growth and grain yields.To date,scarce knowledge is available about nitrogen utilization genes and mechanisms in welsh onion.To gain further insight into the effects of nitrogen treatment,we investigated on transcriptomics as well as amino acids analysis of welsh onion in response to altered nitrogen supply.Approximately 800 genes were differentially regulated with different concentrations of N-fertilizer.GO enrichment analysis revealed that N-mediated processes for metabolism,biosynthesis and transportation of amino acids were highly over-represented.The KEGG analysis also indicated the enrichment pathways were related with amino acids metabolism,with cysteine,beta-alanine,arginine,proline and glutathione being predominant.The DEGs in response to altered nitrogen supply resulted in different contents of amino acids.A close relationship between gene expression and the content of amino acids was revealed.These studies improved the understanding of the nitrogen regulatory network in welsh onion.The key genes increased our knowledge of the mechanism of N usage and guiding the rational use of N-fertilizer for plant improvement.5.Microorganisms are considered to be one of the most sensitive biological indicators.The variation of the Microbial Community Structure and Diversity often indicates the change of the soil environment.In order to research for the variation of soil microbial diversity after the soil of Green onion was treated with three different levels of nitrogen,we used high-throughput sequencing to analyze the V3-V4 region of the 16S DNA gene.A total of 13378,10168 and 9254 OTUs are acquired in the three samples respectively.The result showed that the number of Microorganisms reduced with increasing of nitrogen levels.This trend is samilar to the results of the Rank-abundance curve and alpha diversity index（Chao1,ACE）.At phyla level,in each sample,many of the dominant rhizosphere genera（Proteobacteria,Actinobacteria,Planctomycetes,etc.）displayed different Changing patterns.The trend of Bacteroidetes,Verrucomicrobia is declining with increasing of nitrogen levels.The content of Actinobacteria and Planctom change trend is inverted V shape with the increase of nitrogen.Moreover the trend of Proteobacteria is opposite with the change of Actinobacteria and Planctom.At the level of genus,in the 2b sample,Pseudomonas and Planctomycetes with nitrogen fixation were significantly higher than the 1w and 3q sample conditions.The content of phosphate-dissolving bacteria（Actinobacteria,Flavobacterium）showed a inverted V shape with the increase of nitrogen.This might have guiding significance for the application of nitrogen fertilizer. |
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