Measuring Transpiration Resistance of Leaves

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Abstract
A method, suitable for field use, is given whereby the resistance offered by the leaf anatomy to diffusive loss of water can be measured directly, rapidly, and with simple, portable equipment. A small cup, containing a sensitive humidity sensor, is clamped onto the leaf and the time rate of change of the sensor indication is measured over a short period, often less than 1 minute. Appropriate calibration permits the conversion of the time rate of change to the diffusion resistance inclusive of a temperature correction. Construction details of suitable, portable equipment are supplied. The diffusion resistance, thus measured, can be used to compute the absolute transpiration rate of leaves and plants, and to characterize the movements and responses of stomates with direct reference to the transpiration process. The leaf resistance, as measured directly, can also be used in combination with knowledge of atmospheric transport processes to predict evaporation from plant canopies.