In order to explore the effects of different biostimulants on carbon and nitrogen metabolism of flue-cured tobacco, Zhongyan 100 was used as the material, and four treatments of spraying water (CK), 100 mg/L γ-aminobutyric acid (T1), 100 mg/L chitosan oligosaccharide (T2) and 100 mg/L alginate oligosaccharide (T3) were set up. The biomass, photosynthetic characteristics and carbon and nitrogen metabolism of flue-cured tobacco were analyzed by foliar spraying at the vigorous growth stage and mature stage of tobacco plants. The results showed that, (1) Compared with the control treatment, biostimulant treatment improved the photosynthetic characteristics of tobacco leaves, the net photosynthetic rate increased by 13.2%-33.3%, respectively, and the biomass accumulation of flue-cured tobacco increased. In the vigorous period of carbon and nitrogen metabolism of flue-cured tobacco, the activities of nitrate reductase, glutamine synthetase, neutral invertase and α-amylase in tobacco leaves were significantly increased, and the accumulation and transformation of carbon and nitrogen metabolites in tobacco leaves were promoted.

T1 treatment significantly increased the activity of carbon metabolism enzymes, promoted the accumulation of total sugar and reducing sugar in tobacco leaves, and the expression levels of carbon metabolism genes NtNINV10, NtAMML and NtTPP were significantly up-regulated. T2 treatment significantly increased the activity of nitrogen metabolism enzymes in flue-cured tobacco, promoted nitrogen absorption and nicotine synthesis in flue-cured tobacco, and the expression levels of nitrogen metabolism genes NtNR, NtGS, and NtGDH1 were significantly increased. T3 treatment increased the activity and products of carbon and nitrogen metabolism enzymes in flue-cured tobacco, and significantly increased the expression levels of NtAMML. In summary, spraying different biostimulants significantly promoted the growth and development of tobacco plants. Among them, γ-aminobutyric acid significantly affected the carbon metabolism process of flue-cured tobacco, chitosan oligosaccharide significantly increased the nitrogen metabolism intensity of flue-cured tobacco, and alginate oligosaccharide had a balanced effect on the carbon and nitrogen metabolism of flue-cured tobacco.