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Factors Affecting the Development of Flue-cured Tobacco Grown in Artificial Environments. V. Effects of Humidity and Nitrogen Nutrition¹

Controlled environment rooms (CERs) were used to investigate effects of relative humidity on physical and chemical properties of mature, flue-cured tobacco (Nicotiana tabacum L.) leaves. The relative humidities in separate CERs were monitored with a dewpoint hygrometer and maintained at 90% (high) or 65% (low) relative humidity. Plants were moved between the two CERs to evaluate effects of diurnal and seasonal variations in relative humidity. The apparent effects of humidity on leaf size and shape were dependent on age of the plants. For plants grown in continuous high humidity, leaf sizes were greater at lower and middle stalk positions, but were less at upper stalk positions, than for plants grown in continuous low humidity. The reduction of areas of upper leaves by high humidity was a residual response to the humidity during the initial 3 to 5 weeks after transplanting. Initial periods of high humidity, whether followed by low or high humidity, also resulted in abnormally elongated upper leaves. Furthermore, variations in total plant leaf areas which resulted from diurnal variations in humidity were highly correlated with total nitrogen content in leaf tissues. These results suggest that suppression of nitrogen uptake by high humidity during a critical period of leaf formation was directly involved. Humidity during later stages of growth apparently has effects on the chemical balance within tobacco plants unassociated with nitrogen accumulation. High humidity during the light period tended to increase both starch and alkaloid composition of leaves.

Key Words: Leaf area • Leaf shape • Root growth • Starch • Alkaloids

² Assistant Professor, Dept. of Soil Science, and Research Assistant Engineer, Phytotron, N. C. State Univ., Raleigh, NC 27607.