Effects Of Water And Nitrogen Interaction On Nitrogen Utilization, Nicotine Metabolism, Physiological Characteristics & Yield And Quality Of Flue-cured Tobacco

Tobacco（Nicotiana tabacum L.）is an important cash crop for leaf use in China,which plays a pivotal role in national tax revenue and plays an important role in targeted poverty alleviation.Water and nitrogen are important factors affecting plant photosynthesis,both of which have a great impact on the yield and quality of flue-cured tobacco.In tobacco leaf production,the mismatch of water and nitrogen supply often leads to low utilization rate of water and nitrogen and a series of environmental problems.Therefore,it is necessary to improve the quality of flue-cured tobacco by coordinating water and nitrogen,fixing nitrogen with water and promoting water with nitrogen.In this study,yunyan 99 was used as the material,through pot and field experiments,three soil water conditions W1（soil relative water content 75%～85%）,W2（soil relative water content 55%～65%）,W3（soil relative water content 35%～45%）and three nitrogen application rates N1(4 g·plant^-1),N2(5 g·plant^-1),N3(6 g·plant^-1)effects of nine water and nitrogen interaction treatments combined with two factors on nitrogen utilization,nicotine metabolism,physiological characteristics and yield quality of flue-cured tobacco leaves,in order to provide a theoretical basis for the coordinated application of water and fertilizer and improvement of yield quality of tobacco leaves.The main results obtained are as follows:1.The increase of nitrogen application rate under different soil moisture conditions was beneficial to dry matter accumulation and nitrogen utilization of flue-cured tobacco.Under the same soil relative water content,N3 treatment could increase dry matter accumulation,nitrogen content of organs,Ndff of organs(contribution rate of ¹⁵N absorbed by plant organs from fertilizer to total nitrogen content of organs)and nitrogen use efficiency.The effect of increasing N application was better under W2 condition,in which,compared with W2N1 treatment,dry matter accumulation increased by 7%,N content in root,upper leaf and lower leaf increased by 12.2%,35.1%and 84.6%,respectively,and N use efficiency increased by 22.8%.The increase of soil relative water content under the same nitrogen application rate was beneficial to dry matter accumulation and nitrogen utilization of flue-cured tobacco,and the effect was better under the condition of W1.Comprehensive analysis showed that W1N3,W1N1 and W2N3 had better effects.2.Different water and nitrogen treatments had significant effects on nicotine content and its synthesis in flue-cured tobacco.The effect of nitrogen application rate on nicotine synthesis was different with soil relative water content.At 85 days after transplanting,the content of nicotine in upper leaves of W2N2 and W2N3 treatments increased by 24.1%and57.8%compared with that of W2N1 treatment,respectively.Compared with W3N1treatment,the nicotine content in the middle leaves of W3N2 and W3N3 treatments increased by 37.2%and 56.6%,respectively,and the nicotine content in the lower leaves increased by 27.0%and 39.5%,respectively.The nicotine content in all parts was lower under W1N1 treatment.The activities of arginine decarboxylase（ADC）and ornithine decarboxylase（ODC）under different nitrogen treatments（51 days after transplantation）were significantly different under W2 condition.Compared with W2N1 treatment,the activity of ADC and ODC increased by 10.7%and 21.1%,17.6%and 28.6%,respectively,in W2N2 and W2N3 treatments.By means of metabonomics to nicotine content differences of W1N1,W2N3 processing root differences metabolites analysis results show that the difference of metabolites in amino acyl t RNA biosynthetic pathway,ABC transport pathway,amino acid biosynthesis pathway and significantly enriched in the purine metabolism,nicotine synthesis way significant differences metabolites,The content of aspartic acid and arginine was positively correlated with that of nicotine.3.Under different soil moisture conditions,the appropriate amount of increasing nitrogen fertilizer could increase the content of osmotic regulatory substances in leaves of flue-cured tobacco,improve the antioxidant defense system of flue-cured tobacco,and alleviate the oxidative damage of flue-cured tobacco.Compared with W2N1 treatment,soluble protein and soluble sugar contents in W2N3 treatment were increased by 45.7%and28.5%,superoxide dismutase（SOD）activity was increased by 31.2%and peroxidase（POD）activity by 44.9%,respectively.The increase of nitrogen application rate could effectively reduce the increase of malondialdehyde and superoxide anion free radical content in leaves caused by the decrease of soil water content.Under the same soil water content condition,the effects of N2 and N3 treatments were better.Compared with N1treatment,the malondialdehyde content was reduced by 19.4%in W1N3 treatment,and the superoxide anion free radical content was reduced by 25.1%in W3N3 treatment.4.Different water and nitrogen treatments had significant effects on the yield and quality of tobacco leaves and the content of aromatic substances.Agronomic and economic traits were better treated by N3 under W1 and W2 conditions.Under W3 condition,N2treatment showed better performance.Among them,W1N2 and W1N3 had better treatment effect.The contents of nicotine and total nitrogen were more suitable for N2 treatment under W1 condition.N1 was suitable for nicotine and total nitrogen under W2 condition.The content of nicotine and total nitrogen treated by N3 is more suitable under W3condition.W1N3 treated the cured tobacco leaves with better glucoalkaloid ratio and nitroalkaloid,better chemical composition coordination,W3N3 treated the tobacco leaves with higher content of neutral aromatic substances.Comprehensive analysis showed that N2 and N3 had better treatment effect under W1 condition,N3 had better treatment effect under W2 condition,and N2 had better treatment effect under W3 condition.In conclusion,suitable combination of water and nitrogen can improve the nutrient accumulation of tobacco plant,increase the nicotine content and synthase activity,alleviate the oxidative damage of tobacco,improve the antioxidant defense system of tobacco,thus promoting the growth of tobacco,improving the quality and economic value of tobacco.The effect of N2 and N3 was better in W1 condition,the effect of N3 was better in W2condition,and the effect of N2 was better in W3 condition.The results provided scientific basis and technical support for water-nitrogen coordination in flue-cured tobacco production.