Canadian Forest Service Publications
Effects of pressure increase and release on temperature within a pressure chamber used to estimate plant water potential. 1973. Puritch, G.S.; Turner, J.A. Journal of Experimental Botany 24(2): 342-348.
Issued by: Pacific Forestry Centre
Catalog ID: 28704
Available from the Journal's Web site. †
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During a water-potential measurement sequence, temperature change within the pressure chamber exhibits certain distinct phases. At the introduction of gas into the chamber there is a rapid increase in temperature, normally in excess of 8 °C above ambient, which is directly related to the rate of pressure increase. After reaching a maximum, temperature begins to decline gradually during continued pressure increase, and subsequently falls to ambient after gas entry coases. When pressure is rapidly released from the chamber at the end of a measurement, temperature instantly falls to subzero values.
The causes of these temperature changes are explained in terms of simple thermodynamics, and ways of reducing them are described.