Analysis Of Morphological,Physiological Changes And Transcriptomic Differences Of Walnut (Juglans Regia L.) Rootstock Seedling Induced By Nitrogen

In this study,the walnut rootstock seedlings in Hotan and Aksu provenance were induced by different nitrogen levels.Explore the morphological and physiological characteristics of walnut rootstock seedlings in two provenance sites under different treatments.Determine the optimum combination of nitrogen levels and walnut rootstock seedlings from different provenances.According to the optimum gradient range of nitrogen fertilizer screened in the previous stage,exponential fertilization treatments with different nitrogen concentrations were carried out.Based on the seedling quality of walnut rootstock seedlings and the nitrogen loading capacity,the better nitrogen application rate was selected.In order to guide the standardized fertilization of walnut rootstock seedlings,it will provide a theoretical reference for cultivate walnut seedlings and integrated water and fertilizer precise nitrogen application.In order to explore the molecular mechanism of walnut rootstock seedlings against nitrogen stress,this study analyzed the differences in root morphology,physiology and transcriptomics of walnut rootstock seedlings in nitrogen stress environments.It is expected to provide a theoretical basis for the cultivation of high nitrogen use efficiency（NUE）genotype walnut rootstock seedlings.The research results are as follows:（1）Under the gradient loading of nitrogen,the indicators showed a trend of uplift followed by suppression.When the fertilizer amount reached 10-15 g·plant^-1,plant height and total root volume reached the highest value,plant height:95.27 cm,72.07 cm,root volume:1249.75 cm³,928.01 cm³.The net photosynthetic rate increased with the increase of nitrogen level,and reached the peak value(12.73,12.36 mol·M^-2·S^-1)when the fertilizer amount reached 10 g·plant^-1.After the peak value,the net photosynthetic rate gradually decreased with the increase of nitrogen level.Nitrate reductase activity and soluble protein content showed a trend of increase and then decrease,and reached the highest value at 15 g·plant^-1.According to the comprehensive evaluation,it was preliminarily concluded that the morphology and physiological characteristics of walnut rootstock seedlings in the two provenance fields cultivated in the field soil environment increased with the increase of nitrogen level,and reached the maximum value at 10-15g·plant^-1,and the subsequent treatment would inhibit the morphology and physiological characteristics of walnut rootstock seedlings.（2）After the index fertilization treatment,the activity of key enzyme of nitrogen metabolism and the content of amino acid and protein showed a trend of first increasing and then decreasing with the increase of nitrogen level.With the increase of nitrogen level,the accumulation of P and K gradually decreased after the nitrogen induction of 8 g·plant^-1,indicating that the luxury consumption and toxicity of N nutrients inhibited the accumulation of P and K nutrients.After the induction of index fertilization,based on the morphological characteristics,nitrogen metabolism characteristics and nutrient load of walnut rootstock seedlings,it was concluded that the recommended nitrogen application range of walnut rootstock seedling cultivated by matrix container was 6-8 g·plant^-1.（3）The content of nitrate,ammonium and total nitrogen in the root system was proportional to the gradientof nitrogen.The contents of protein,total amino acid,MDA,PRO,IAA and GA3 showed a v-shaped change with the increase of nitrogen gradient.The content of ZA and ABA showed an upward trend.According to the analysis of transcriptomic data,the abundance of CRY1,LHY,RVE and LAX2 genes changed due to nitrogen stress.Based on the analysis of gene co-expression network,we speculated that the root system of walnut rootstock could resist the damage caused by nitrogen stress through the"Circulatory Regulation Model of the Co-expression network of Nitrogen metabolism-Circadian rhythm"（CRMCNC）.Namely nitrogen metabolites,free of NO₂^--N signals or Glu in promoting CRY1 gene expression in the nuclei,phase shift in the biological clock,produced a response to N,RVE genes through regulating hormone signal transduction network will stimulate response to information transmission to nitrogen metabolic pathways,control key enzyme activity of nitrogen metabolism,reduce the accumulation of NO₃^-and NH₄⁺,thus reducing poison of cell nutrients.