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Growth and Nitrogen Accumulation in Tobacco Plants as Affected by Nitrate Concentration, Root Temperature, and Aerial Temperature¹

Early spring is a period of widely fluctuating gradients between aerial and soil temperatures. Aerial temperatures affect growth and N demand of seedlings while temperature and N availability in the root zone alter the ability of roots to supply the plant with N. The purpose of this study, in which tobacco (Nicotiana tabacum L.) plants were grown in a temperature controlled, flowing nutrient solution system within a controlled-environment room, was to determine the independent effects of aerial temperature, root-zone temperature, and NO₃^- concentration of nutrient solution and their interactions on growth and N accumulation. In each of nine experiments consisting of all combinations of day/night aerial temperatures of 22/18, 26/22, and 30/26 C and solution NO₃^- concentrations of 3.5, 7.2, and 14.6 mM, plants were grown for 38 days at root-zone temperatures of 16, 24, and 32 C. For analysis of variance the study was considered as a 3³ factorial. Plants were sampled at 14, 19, 24, 31, and 38 days, dried, weighed, and analyzed for total N and soluble carbohydrates.

Root-zone temperatures had greater effects on growth than either aerial temperature or NO₃^- concentration. Plant dry weight, leaf area, and stem height were less at 16 C than 24 and 32 C root temperatures. The reduction in growth at 16 C apparently was attributable to initial water stress and reduced loading of N from the root into the vascular system. Reductions in dry matter and N accumulation of plants associated with reductions in root temperature were enhanced as aerial temperature was increased and solution NO₃^- concentration was decreased. This suggests an interrelated and synergistic effect of the variables.

Key Words: Leaves • Nicotiana tabacum L. • Roots • Soluble carbohydrates

² Former graduate research assistant and associate professor, Dep. of Soil Science, North Carolina State Univ., Raleigh, NC 27650.

Received for publication July 11, 1980.