CHAPTER 12 MEASUREMENTS WITH THE MINI-PAM
This expression, which was introduced by Genty et al. (1989) is
identical to the YIELD-parameter measured by the MINI-PAM (see
12.3.7). With this fluorometer, YIELD-determination has become
exceedingly simple: The fiberoptics are held at short distance (ca. 10
mm) to a sample, and the START-key is pressed. Everything else is
proceeding automatically within seconds:
• the present fluorescence yield F is sampled
• a saturation pulse is applied
• Fm' is sampled (displayed as ... M)
• YIELD = (Fm'-F)/Fm' is calculated and shown on the LC-display
• the obtained data are stored in the MEMORY.
The simplicity of this measurement is contrasted by the profound
information it provides. In steady-state illumination, as prevailing
under field-conditions, the YIELD-parameter reflects the efficiency
of the overall process. Any change at the various functional levels
(outlined at the start of this section) will be reflected in this
parameter. The accuracy of this measurement is very high, and as
recordings are quick, very detailed information on the photosynthetic
performance of plants under varying environmental and
physiological conditions can be obtained.
For full assessment of fluorescence information, knowledge of
environmental parameters is required, in particular of light intensity
and temperature. For example, if the measured YIELD of leaf A is
lower than that of leaf B, this does not necessarily mean that leaf A is
photosynthetically less competent than leaf B. The difference could
as well arise from leaf A being exposed to stronger light or to a lower
temperature than leaf B. The MINI-PAM offers the possibility to
measure photosynthetically active radiation (PAR) and temperature
at the same spot of a leaf where also fluorescence is measured (see
62
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