Leaf Temperatures in a Gas Exchange Chamber and in the Open Air

Leaf temperatures in a Koch fully climatized gas-exchange chamberas designed by Siemens and in a similarly equipped open-airreference were measured with horizontally and vertically insertedthermocouples on Nerium oleander L. On a sunny day with onlylittle air movement and an average air temperature of 20.4 °C,leaf over-temperatures in the gas-exchange chamber were loweron average by 2.2 K. The extent of reduction of over-temperaturein the chamber is determined by the reduced global radiationin the chamber and the differences of wind velocities in chamberand reference. Differences in the ventilation intensity in thechamber have no demonstrable influence on the leaf over-temperatures.The over-temperatures of the reference leaves, on the otherhand, depend to a large degree on air velocity. The changedradiation and air flow conditions in the chamber as comparedwith open-air conditions have consequences for the physiologicalreactions of the enclosed plant and must be taken into accountwhen comparing results from gas-exchange measurements with open-airconditions. For further improvements of gas-exchange measurementequipment, air flow conditions and radiation quantity and qualitymight be starting points