Photosynthesis Research

, Volume 9, Issue 3, pp 345–357

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

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

Abstract

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 

Abbreviations

A

CO2 assimilation rate

Amax

Maximum rate of CO2 assimilation

Aopt

Optimum teperature for CO2 assimilation

CTWB

Controlled-temperature water bath

DPC

Dew point controller

E

Transpiration rate; gl, leaf conductance

HCC

Humidity control circuit

IRGA

Infrared gas analyzer

LT

Leaf temperature

LTC

Leaf temperature controller

MFC

Mass flow controller

QFD

Quantum flux density

RH

Relative humidity

RHC

Relative humidity controller

VPD

Vapour pressure difference

ΔCO2

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
  2. 2.Shimadzu Seisakusho LTDKyotoJapan

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