Observing and Recording Leaf Gas Exchange
CIRAS-2 Operator's Manual Version 2.04
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If this occurs, simply wait until the completion of the Zero or Diff Bal check.
Placing the Leaf in the Cuvette
Choose leaves of sufficient size to completely fill the cuvette head opening around the gasket (as
illustrated below). The built-in IR leaf temperature sensor will return false values if light enters from gaps
around the leaf. In other words, the IR sensor must “see” only the lower leaf surface, otherwise you must
select „Energy Balance‟ as the default Leaf Temperature Determination type.
The leaf blade may extend beyond the foam gasket surrounding the opening. However, the leaf blade
must not extend beyond the back of the lower metal plate, i.e. into the back of the cuvette‟s lower jaw,
where part of the leaf will be crushed when the cuvette is closed. Try approaching the leaf from the side
with the open cuvette to avoid accidentally injuring the leaf in this way.
The cuvette tension screw is located beneath the cuvette open/close lever. Use a small hex wrench to
adjust the screw tension if needed to accommodate leaves of varying thicknesses. Turn the screw
counter-clockwise to tighten and clockwise to loosen the tension. Normally no more than ¼ turn in either
direction is needed. The goal is to establish a good seal without i) causing extreme pressure on the leaf
or ii) allowing ambient air to leak around the foam gaskets.
With the leaf enclosed in the cuvette you should quickly notice a series of dynamic leaf responses,
assuming ideal physiological conditions. Sub-stomatal CO
2
concentration (Ci) will begin dropping, after
being initially higher than the reference CO
2
concentration (Cr). When Ci<Cr there is an instantaneous
change in net photosynthesis (Pn) values from a negative rate (respiration) to a positive rate.
Simultaneously, the differential CO
2
concentration (Cd) will go into negative values while differential
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