Effects of Heat on the Physiology of Seedlings of Eucalyptus obliqua

Abstract

Seedlings of E. obliqua L'Herit. were heated in air at different temperatures for various times. Mortality was assessed using a wide-range a.c. bridge, and the internal temperatures of the upper and lower stems and leaves were monitored. The extent of killing depended on both the temperature and the duration of heat. No killing occurred at 40°C and total killing occurred at 100°C; at intermediate temperatures, the extent of killing was a function of duration of treatment. The temperature inside the lower stem declined for 20 min after applying heat, followed by a gradual increase in parallel with the increase in temperature of the soil. This effect was attributed to the movement of water from the roots and soil into the lower stem, and could explain the capacity of seedlings of E. obliqua to survive a temperature of 80°C, which is higher than reported for other species.