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Aimed to explore the ecological reasons for the difference in nicotine content of flue-cured tobacco planted in different regions of Hunan Province, field experiments were conducted in Sangzhi, Liuyang, and Yongzhou counties, the three typical tobacco regions of Hunan Province, taking tobacco variety K326 as the test object. Simultaneously, pot experiments with local soils and guest soils were carried out. The nicotine content of mid position tobacco leaves was analyzed at harvest time. Field experiments showed that the average nicotine content of tobacco leaves differed significantly among test sites, with that in Sangzhi being the highest, followed by Liuyang, and Yongzhou. Pot experiments showed that climate had significant effects on the average nicotine content of tobacco leaves, while soil and its interaction with climate had less effects. The contribution rate of climate, soil, and their interaction on the variance of the average nicotine content was 60.0%, 12.8% and 27.2%, respectively. The main sub-ecological factors closely related to the average nicotine content of flue-cured tobacco planted in different regions of Hunan Province were in turn the cloud cover at maturing stage, the relative humidity, sunshine hours, diurnal temperature variance, and rainfall at root-extending stage, and the average air temperature at vigorous growth stage. Generally, climate was the main ecological factor that led to the nicotine content difference of flue-cured tobacco planted in different regions of Hunan Province.

A pot experiment with the soils from Yongzhou, Liuyang, and Sangzhi, the high-quality tobacco planting regions of Hunan Province, was conducted to study the effects of climate, soil, and their interaction on some neutral volatile aroma components in flue-cured tobacco leaves. The contents of test neutral volatile aroma components in the flue-cured tobacco leaves were of medium variation, and the variation intensity was decreased in the order of dihydroactinolide, damascenone, furfural, total megastigmatrienone, and beta-ionone. Climate, soil, and their interaction affected the neutral volatile aroma components in different degrees. The furfural content was most affected by climate, the damascenone content was most affected by climate and by soil, the total megastigmatrienone and beta-ionone contents were most affected by the interaction of soil and climate, while the dihydroactinolide content was less affected by soil, climate, and their interaction. The contribution of climate, soil, and their interaction to the contents of the five aroma components was 40.82%, 20.67%, and 38.51%, respectively. During different growth periods of tobacco, different climate factors had different effects on the neutral volatile aroma components. The rainfall, cloudiness, and mean air temperature at rooting stage, the diurnal temperature amplitude, sunshine time, and evaporation at vigorous growth stage, and the rainfall, evaporation, and mean air temperature at maturing stage were the top three climate factors affecting the contents of the neutral volatile aroma components in flue-tobacco leaves. For the soil factors, the available potassium, available phosphorus, and pH were the top three factors affecting the contents of the five components.