Effects of Nitrogen Application Rates on Quality and Carbon-Nitrogen Metabolism Enzymes of Middle Leaves in Flue-Cured Tobacco

Zhang Jiacheng; Li Panpan; Wang Zhuangzhuang; Si Hongyang; Wang Zhihui; Fu Bo; Zhang Xiaogang; Li Xinkai; Zhao Mingqin

doi:10.14083/j.issn.1001-4942.2026.03.012

Abstract：To clarify the growth,metabolism and quality response rules of different flue-cured tobacco genotypes under varying nitrogen application levels,a two-factor randomized block design was adopted with three nitrogen levels of low(N6,90 kg·hm-2),medium(N7,105 kg·hm-2),and high(N8,120 kg·hm-2),and two cultivars,Yunyan 99 and Yunyan 119,were used as materials in the experiment.Agro-nomic traits,chlorophyll content and net photosynthetic rate of middle leaves were measured at multiple growth stages,along with the activities of carbon and nitrogen metabolism enzymes.Conventional chemical compo-nents,aroma constituents,appearance quality and economic traits were determined in both fresh and cured leaf samples.The results were as follows.① From 60 to 90 days after transplanting,the agronomic traits and photosynthetic indicators showed different change with the increase of nitrogen application rates.Yunyan 99 performed better at N8,while Yunyan 119 was superior at N7.② From 60 to 75 days after transplanting,theβ-amylase(β-AL)activity in Yunyan 99 leaves increased with the increase of nitrogen rate,while that in Yu-nyan 119 leaves increased first and then decreased;the activity of neutral invertase(INV)and glutamine syn-thetase(GS)reached the peak after 60 days of transplanting;the nitrate reductase(NR)activity increased first and then decreased,which was higher at 60 to 75 days and then reduced.Significant effects of cultivar and its interaction with nitrogen rate were observed on the activity of the four enzymes.③ In cured leaves,the reducing and total sugar contents and the sugar-to-nicotine ratio decreased with increasing nitrogen application rate,while the nicotine and total nitrogen contents increased;the potassium-to-chlorine ratio generally excee-ded the favorable threshold of 4.④ Regarding aroma,the content of pigment degradation products increased with the increase of nitrogen rate in Yunyan 99,but decreased in Yunyan 119;the total aroma content of Yuyan 99 was the highest at N8 level,and that of Yunyan 119 was the highest at N7 level.⑤ Correlation a-nalysis indicated that the activity of the carbon and nitrogen metablism enzymes were significantly or very sig-nificantly correlated with the total and reducing sugar contents,nicotine content,sugar-to-nicotine ratio and potassium-to-chlorine ratio in cured leaves,indicating that nitrogen application influenced chemical coordina-tion and aroma quality through regulating carbon-nitrogen metabolism and pigment degradation.Overall,based on growth,metabolism and quality indices,N8(120 kg·hm-2)should be recommended for Yunyan 99 and N7(105 kg·hm-2)for Yunyan 119.The results could provide a reference for nitrogen management for good-quality middle leave production in the Xunyang tobacco-growing region.