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A Portable Instrument for Rapidly Measuring Conductance and Transpiration of Conifers and Other Species

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An improved porometer has been constructed which facilitates the determination of leaf conductance and transpirational flux density on conifers and other species with irregularly shaped foliage. The porometer is stirred and utilizes a full-range, fast-responding relative humidity sensor to measure ambient relative humidity and conductance near ambient humidity. Automatic timing and digital readout minimize operator errors. The unit is rapid, light in weight (3.2 kg total), and has been durable in a variety of environmental conditions, thus making it ideal for field research requiring numerous measurements. An evaluation of adsorption of water vapor on the interior surfaces of the porometer indicated maximum adsorption at high ambient relative humidities and low temperatures (e.g., about 75 percent adsorption at 75 percent relative humidity and 16°C). Typical diurnal changes of needle conductance of Monterey pine were observed at two levels of soil water supply, with lower conductances when soil water was limiting. Transpirational flux density of citrus seedlings, calculated using porometer and leaf temperature data (conductance X absolute humidity difference from leaf to air), agreed well with flux densities calculated from pot weight changes. Thus the absolute accuracy of conductances and transpiration rates calculated from porometer data seems to be acceptable. Forest Sci. 23:227-237.

Keywords: Porometer

Document Type: Journal Article

Affiliations: Staff Research Associate, Department of Plant Sciences, University of California, Riverside, CA 92521

Publication date: June 1, 1977

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