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This article in AJ

  1. Vol. 68 No. 6, p. 872-875
     
    Received: Oct 4, 1975
    Published: Nov, 1976


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doi:10.2134/agronj1976.00021962006800060009x

Performance of the Silver-foil Psychrometer for Measuring Leaf Water Potential in situ1

  1. Glenn J. Hoffman and
  2. Anthony E. Hall2

Abstract

Abstract

Continuous in situ measurements of leaf water potential are often needed in studies of the soil-plant-atmosphere continuum. The development of the silver-foil thermocouple psychrometer has made these measurements possible. The objective of this investigation was to evaluate the performance of the silver-foil psychrometer under various steady-state and dynamic conditions. Leaf water potential measurements were made in situ on pinto bean (Phaseolus vulgaris L.) in a controlled-environment plant chamber where temperature, relative humidity, CO2 concentration, radiation, and photoperiod were precisely controlled.

Typically, the psychrometer will reach equilibrium with an intact leaf 2 hours after attachment. Consistent leaf water potentials are attainable when the leaf temperature varies by as much as 0.25 C/min. This thermal stability is as good as that of any multijunction psychrometer described to date. At radiation levels below 50 Wm−2, leaf water potential readings can be made on unshaded leaves; above this level, the leaf must be shaded to prevent thermal gradients across the leaf and psychrometer.

The silver-foil psychrometer responded to rapid oscillations in leaf water potential. During oscillations, leaf water potential preceded leaf conductance and transpiration by one-third of the oscillation period. Net photosynthesis oscillated in phase with leaf conductance, indicating that net photosynthesis is limited by the internal CO2 concentration, even at very low irradiances.

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