Abstract

Growth of tree-of-heaven (Ailanthus altissima (Mill.) Swingle) seedlings was evaluated during a 28-day exposure to constant root-zone temperatures of 18°, 24°, 30°, and 36°C (64°,75°, 86°, and 97°F). Leaf area, stem length, root-to-shoot ratio, and shoot and root dry weights were greatest among plants with 24°C (75°F) root zones. Diminished growth among plants at high root-zone temperatures was associated with reduced leaf conductance. After 14 days of treatment, leaf diffusive resistance of plants in the 36°C (97°F) regime was eight times greater than that of plants with 24°C (75°F) root zones. Regulation of leaf gas exchange among plants with 36°C (97°F) root zones probably contributed to the maintenance of moderate leaf water potentials but limited the fixation of carbon necessary to sustain growth.