Photosynthesis Research

, Volume 9, Issue 3, pp 345–357 | Cite as

A system for measuring leaf gas exchange based on regulating vapour pressure difference

  • Waichi Agata
  • Yoshinobu Kawamitsu
  • Susumu Hakoyama
  • Yasuo Shima
Regular paper


A system for measurement of leaf gas exchange while regulating leaf to air vapour pressure difference has been developed; it comprises an assimilation chamber, leaf temperature controller, mass flow controller, dew point controller and personal computer. A relative humidity sensor and air and leaf temperature sensors, which are all used for regulating the vapour pressure difference, are mounted into the chamber. During the experiments, the computer continuously monitored the photosynthetic parameters and measurement conditions, so that accurate and intenstive measurements could be made.

When measuring the light-response curve of CO2 assimilation for single leaves, in order to regulate the vapour pressure difference, the leaf temperature and relative humidity in the chamber were separately and simultaneously controlled by changing the air temperature around the leaf and varying the air flow rate through the chamber, respectively. When the vapour pressure difference was regulated, net CO2 assimilation, transpiration and leaf conductance for leaves of rice plant increased at high quantum flux density as compared with those values obtained when it was not regulated.

When measuring the temperature-response curve of CO2 assimilation, the regulation of vapour pressure difference was manipulated by the feed-forward control of the dew point temperature in the inlet air stream. As the vapour pressure difference was regulated at 12 mbar, the maximum rate of and the optimum temperature for CO2 assimilation in rice leaves increased 5 μmolCO2 m−2 s−1 and 5°C, respectively, as compared with those values obtained when the vapour pressure difference took its own course. This was reasoned to be due to the increase in leaf conductance and the decrease in transpiration rate. In addition, these results confirmed that stomatal conductance essentially increases with increasing leaf temperature under constant vapour pressure difference conditions, in other words, when the influence of the vapour pressure difference is removed.

This system may be used successfully to measure inter- and intra-specific differences and characteristics of leaf gas exchange in plants with a high degree of accuracy.

Key words

control measurement photosynthesis vapour pressure difference 



CO2 assimilation rate


Maximum rate of CO2 assimilation


Optimum teperature for CO2 assimilation


Controlled-temperature water bath


Dew point controller


Transpiration rate; gl, leaf conductance


Humidity control circuit


Infrared gas analyzer


Leaf temperature


Leaf temperature controller


Mass flow controller


Quantum flux density


Relative humidity


Relative humidity controller


Vapour pressure difference


Difference of CO2 concentration between inlet and outlet air


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Copyright information

© Martinus Nijhoff/Dr W. Junk Publishers 1986

Authors and Affiliations

  • Waichi Agata
    • 1
  • Yoshinobu Kawamitsu
    • 1
  • Susumu Hakoyama
    • 1
  • Yasuo Shima
    • 1
  1. 1.Department of Agriculture, Faculty of AgricultureKyushu UniversityFukuokaJapan

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