Determination of stomatal conductance by means of infrared thermography

The leaf energy balance equation is extended to obtain the boundary layer resistances to heat transfer and the stomatal resistance, the stomatal conductance respectively, of leaves in vivo. Calculations are based on the determination of temperature rise and fall times (thermal time constants of leaves in different states) which are caused by a sudden change of irradiation intensity. The change in the irradiation was performed by turning on/off a laser diode (675 nm). To measure the temperature and its changes without direct contact with the leaves, a commercial IR-imaging system (thermo-camera) was employed. Experiments were made on ivy leaves under laboratory conditions. The advantages and the applicability of the new method are demonstrated and experienced experimental difficulties are discussed.