Use of thermography for quantitative studies of spatial and temporal variation of stomatal conductance over leaf surfaces

This paper describes a new approach to the calibration of thermal infrared measurements of leaf temperature for the estimation of stomatal conductance and illustrates its application to thermal imaging of plant leaves. The ap proach is based on a simple reformulation of the leaf energy balance equati on that makes use of temperature measurements on reference surfaces of know n conductance to water vapour. The use of reference surfaces is an alternat ive to the accurate measurement of all components of the leaf energy balanc e and is of potentially wide application in studies of stomatal behaviour. The resolution of the technique when applied to thermal images is evaluated and some results of using the approach in the laboratory for the study of stomatal behaviour in leaves of Phaseolus vulgaris L. are presented. Conduc tances calculated from infrared measurements were well correlated with esti mates obtained using a diffusion porometer.