Effects Of Different Nitrate-ammonium Nitrogen Ratios On Nitrogen Uptake And Physiological Metabolism Of Flue-cured And Burley Tobacco

Flue-cured tobacco and burley tobacco were the two main types of tobacco,but there were significant differences in the nitrogen efficiency and nitrate nitrogen content of tobacco leaves between them.With a view to investigating the formation and specific performance of these differences,different ratios of nitrate to ammonium nitrogen were set up at the Research Center for Tobacco Harm Reduction,Henan Agricultural University,from 2020 to 2022.To study their effects on the growth and development of flue-cured tobacco and burley tobacco at seedling stage,ion absorption by roots,root transcription group and chemical composition of burley tobacco after air-curing.Comparison of nitrate and ammonium nitrogen uptake and utilization and differences in physiological metabolism between flue-cured tobacco and burley tobacco.The main results of the research were as follows:1.The indoor pot experiment of flue-cured tobacco and burley tobacco showed that:（1）Nitrate reductase（NR）and glutamine synthetase（GS）activities of flue-cured tobacco were the highest when the nitrate-ammonium nitrogen ratio was 75:25.The NR activity of burley tobacco was the highest when the nitrate-ammonium nitrogen ratio was 50:50,and GS activity was the highest when the nitrate-ammonium nitrogen ratio was 25:75.The total sugar contents of flue-cured tobacco and burley tobacco were the highest（8.22% and 5.36%,respectively）,when the nitrate-ammonium nitrogen ratio was 50:50.（2）The nitrate contents in leaves of burley tobacco and flue-cured tobacco were the lowest(343.73mg·g^-1and 116.77mg·g^-1,respectively),when the nitrateammonium nitrogen ratio was 50:50.（3）Ten indexes including shoot dry weight,total pigment content,nitrate reductase activity,glutamine synthetase activity,leaf total nitrogen content,leaf nitrogen accumulation,total sugar content,soluble sugar content,reciprocal nitrate content,leaf NH₄⁺-N content were comprehensively evaluated based on the principal component analysis.The flue-cured tobacco had the highest score when nitrate-ammonium nitrogen ratio was 75:25,and burley tobacco had the highest score when nitrate-ammonium nitrogen ratio was 50:50.2.The experiment on root absorption kinetics of flue-cured tobacco and burley tobacco hydroponic seedlings showed that:（1）Among the parameters related to absorption kinetics,for NO₃^-,the V_max and V_max/K_m values of burley tobacco were significantly lower than those of flue-cured tobacco,and the K_m and C_min values were significantly higher than those of flue-cured tobacco.For NH₄⁺,under the treatment of NO₃^-: NH₄⁺=50:50,the V_max,K_m and C_min values of burley tobacco were significantly lower than those of flue-cured tobacco.（2）NR and GS activities of burley tobacco roots were significantly lower than those of flue-cured tobacco in each treatment.Under the treatment of NO₃^-: NH₄⁺=100:0,the NR activities of flue-cured tobacco and burley tobacco were the highest,159.15 nmol·min^-1·g^-1 and 136.81 nmol·min^-1·g^-1,respectively.Under the treatment of NO₃^-: NH₄⁺=50:50,the GS activities of flue-cured tobacco and burley tobacco were the highest,1.84 μmol·h^-1·g^-1 and 1.61 μmol·h^-1·g^-1,respectively.（3）Nitrate content in the root and overground part of burley tobacco was significantly higher than that of flue-cured tobacco under each treatment.Under the treatment of NO₃^-: NH₄⁺=0:100,the nitrite content in the roots of flue-cured tobacco and burley tobacco was the lowest,7.67 mg·g^-1 and 9.13 mg·g^-1,respectively.The NO₃^-: NH₄⁺=0:100 treatment had the lowest nitrate content in the overground part of the fluecured tobacco,15.06 mg·g^-1.The NO₃^-: NH₄⁺=50:50 treatment had the lowest nitrate content in the overground part of the burley tobacco,22.95 mg·g^-1.（4）The differentially expressed genes in the flue-cured tobacco root system were more than those in burley tobacco in each treatment.The higher ratio of nitrate and ammonium nitrogen increased the co-expression of differential genes and nitrogen metabolism pathway genes between flue-cured tobacco and burley tobacco.Under each treatment,the glutamine synthetase gene,GLN1^-1 has low expression in burley tobacco.The genes responsible for nitrate absorption and transport,NRT2.6 and NRT2.1 has high expression in the root system of flue-cured tobacco were higher,NRT2.5 has high expression in the root system of burley tobacco was higher,NRT2.4 has high expression in the root system of both flue-cured tobacco and burley tobacco.3.The pot experiment of burley tobacco showed that:（1）Increasing the ratio of ammonium nitrogen and reducing the amount of nitrogen can both reduce the nitrate content in the main vein and leaves of burley tobacco after air treatment.T1: NO₃^-: NH₄⁺=70:30,T2: NO₃^-: NH₄⁺=40:60,T3:NO₃^-: NH₄⁺=40:60 and the total amount of nitrogen is reduced by 10%.The nitrate content in the middle leaf blade of burley tobacco was 1.25 mg·g^-1,0.69 mg·g^-1,and 0.40 mg·g^-1,respectively,and that in the main vein of the middle leaf was 5.15 mg·g^-1,2.37 mg·g^-1,and 1.24 mg·g^-1,respectively.（2）Increasing the ratio of ammonium nitrogen and reducing nitrogen application could both reduce the Tobacco specific nitrosamines（TSNA）content in tobacco leaves.Under T1～T3 treatment,the total four TSNA contents in the middle leaves of burley tobacco were 221.36 ng·g^-1,167.23 ng·g^-1 and 145.03 ng·g^-1,respectively.（3）The total nitrogen content in the upper leaves was the highest in the T1 treatment,3.40%;the total nitrogen content in the middle leaves was the highest in the T2 treatment,3.69%;The total nitrogen content in the lower leaves was the highest in the T2 treatment,3.48%.（4）Increasing the amount of ammonium nitrogen would increase the nicotine content in burley tobacco leaves.On this basis,reducing nitrogen use would reduce the nicotine content of tobacco leaves.The nicotine content in burley tobacco leaves under T1～T3 treatments was 3.89%,4.12% and 4.06%,respectively.The comprehensive research results showed that flue-cured tobacco and burley tobacco had different preferences for nitrate-ammonium nitrogen.Flue-cured tobacco preferred nitrate nitrogen while burley tobacco preferred ammonium nitrogen.When fertilizing in production,the ratio of nitrate-ammonium nitrogen could be adjusted to 75:25 for flue-cured tobacco and 50:50 for burley tobacco.