Leaf Temperature Measurement and Control in a Gas-Exchange Cuvette

Leaf temperature was determined using 0.025-mm junction-welded and 0.125-mm beaded thermocouples. The use of fine-wire thermocouples was necessary to avoid errors in measurement that exceeded 2.5 degrees C in well-watered and 3.5 degrees C in water-stressed plants when using beaded thermocouples. Evanohm was used instead of copper to form one component of the fine wire thermocouple as it is stronger and has a lower thermal conductivity. A cuvette was designed and constructed that allowed for gas exchange to be studied as a function of water potential. A high velocity air ventilation system was used to offset the rise in leaf temperature associated with stomatal closure at low water potentials. This also provided a steady, low, reproducible boundary layer resistance of approximately 0.05 sec cm −1 .