CHAPTER 12 MEASUREMENTS WITH THE MINI-PAM
characteristics of photosynthesis. LIGHT CURVES measured during
the course of a day (e.g. triggered by the Repetition Clock, see
12.3.12) may show largely different characteristics due to the fact
that the physiological state of the photosynthetic apparatus is
regulated by environmental factors in a highly dynamic manner.
Whereas for proper recording of a conventional light response curve
it is essential that all conditions (like temperature, CO
2
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concentration, humidity) are kept constant over extended periods of
time, LIGHT CURVES are sufficiently fast that they can characterize
a momentary state of a plant in a naturally changing environment.
12.3.10 YIELD- and ETR-averaging (menu point 11)
With normal samples under standard conditions the signal/noise
ratio obtained with the MINI-PAM is rather high, such that a single
measurement results in the reliable determination of YIELD and
ETR (see 12.3.7). In practice, the averaging function is most useful
in order to obtain representative information on the photosynthetic
performance of a heterogeneous sample. For example, repeated
measurements at one particular sample site may give YIELD- and
ETR-values fluctuating by no more than 0.001, whereas the values at
another site may differ by more than 0.1 units. This is particularly
true for outdoor measurements where the effective incident light
intensity depends strongly on sample position, possible shading etc.
In order to assess the effective quantum yield and the apparent
electron transport rate of a sample in a given situation under natural
conditions, the sample holder ideally must be attached such that there
is no sample shading. As this ideal can be only more or less
approached, unavoidably there is some variability in the results, and
averaging can be useful. The averaged data are not stored in the
memory. On the other hand, as every individual data set is stored in
MEMORY, which can be later transferred to a PC (see 9), users may
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