Effects of nighttime temperature increase on physio-chemical properties, yield and quality of flue-cured tobacco in high-altitude region of Yunnan Province

This study used tobacco cultivars of 'Yunyan 87' and 'K326' to analyze the effect of nighttime temperature increase on physio-chemical properties, yield and quality of flue-cured tobacco in high altitude region of Yunnan Province. Through field experiment, the study evaluated the effects of nighttime temperature rise on the physical characteristics, chemical composition, micronutrients contents, economic characteristics, and sensory quality of tobacco. The study aimed to explore and improve the physical and chemical properties as well as inherent quality of flue-cured tobacco by the adjustment of ecological factors (temperature in this study). Based on the single factor randomized block design pot experiment, two temperature treatments were established. The first temperature treatment was to artificially keep warm at nighttime (18:00-6:00) under greenhouse condition. During this treatment, average nighttime temperature in the greenhouse was maintained at 16.7 ℃. The second temperature treatment was to keep a natural temperature in the greenhouse for purpose of comparison. In this treatment, the average natural temperature at night was 15.5 ℃. The study showed that rising nighttime temperature broadened the upper leaves and lengthened the lower leaves of 'K326' and 'Yunyan 87'. It also significantly increased single leaf weight and equilibrium moisture content of the upper leaves along with the single leaf weight of the middle leaves of 'K326'. With the rise in nighttime temperature, leaf thickness significantly decreased for the middle and upper leaves of 'K326' and the middle and lower leaves of 'Yunyan 87'. Also leaf stem content significantly decreased for all the leaves of 'K326' and the upper leaves of 'Yunyan 87'. Compared with those under natural nighttime temperature treatment, the contents of total sugar, reducing sugar and total nitrogen increased drastically in the middle and upper leaves of 'K326' under increased nighttime temperature treatment. Also the contents of total nitrogen and potassium increased in all the leaves of 'Yunyan 87'. However, decreases in the contents of nicotine and potassium in the middle and upper leaves of 'K326' were noted. Also the decreases in the total nitrogen in the lower leaves of 'K326', in the contents of total sugar, reducing sugar and nicotine in the upper leaves of 'Yunyan 87', in the content of nicotine in the middle leaves of 'Yunyan 87', and in the contents of total sugar and reducing sugar in the lower leaves of 'Yunyan 87' were observed too. Under nighttime temperature increase treatment, the contents of Zn and Cu significantly decreased while those of Fe and Mn increased in the upper and lower leaves of 'K326', compared with those under the natural temperature treatment. Also the contents of Zn, Cu, Fe and Mn increased in the upper leaves of 'Yunyan 87'. Compared with the natural temperature treatment, nighttime temperature increase treatment improved output, output value, average price and fine tobacco proportion of 'K326' respectively by 252.5 kg·hm^-2, 7 290 Yuan·hm^-2, 1.7 Yuan·kg^-1 and 6.54%. Similarly, these variables of 'Yunyan 87' increased respectively by 100.5 kg·hm^-2, 5 315 Yuan·hm^-2, 2.1 Yuan·kg^-1 and 4.65%. Thus increasing nighttime temperature significantly improved the physical characteristics, chemical component, production output and industrial value of flue-cured tobaccos in high altitude region of Yunnan Province.