A Handpiece for the Simultaneous Measurement of Photosynthetic Rate and Leaf Diffusive Conductance: I. DESIGN

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Abstract
The design and construction of a handpiece for the simultaneous measurement of photosynthetic rate and diffusive conductance of cereal leaves in almost natural conditions in the field is described. Photosynthetic rate is found from the assimilation of 14CO2 by part of the leaf which is temporarily enclosed in a small hand-held chamber. This chamber also acts as a stirred, steady-state water vapour diffusion porometer, allowing the simultaneous measurement of relative humidity from which the leaf diffusive conductance is estimated. The instrument also measures the leaf and air temperatures and incident photon flux density. The important criteria of the performance of such a handpiece are discussed, and the sensors which measure the physical variables of humidity, temperature, and photon flux density are described. An automatic sequencing system built from logic circuits which displays the measured values of these variables and times the operations is also described.

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