CHAPTER 8 COMPONENTS OF THE MINI-PAM
is cut off, the absolute values of actinic light intensities are lower
than in the standard instrument version and in order to obtain
equivalent PAR-values, correspondingly higher intensity settings
must be chosen.
• Spectral shifts:
It is an unavoidable property of halogen light sources that the
emission spectrum shifts from red to blue when the light output
increases with increasing power. This property may complicate
the assessment of photosynthetically active radiation and
consequently of relative electron transport rate (ETR) as well. As
the red part of the spectrum is not used in the MINI-PAM/B, this
aspect is less problematic than in the standard instrument
version.
• Chlorophyll excitation:
In most photosynthetic organisms blue light excites chlorophyll
fluorescence about as well as red light. However, in organisms
with phycobilisomes (cyanobacteria and red algae) the yield of
blue light excited fluorescence is rather low. This is due to the
fact that most of the chlorophyll in these organisms is associated
with photosystem I and in a low-fluorescent state. Therefore, the
use of the blue instrument versions cannot be recommended for
the study of such organisms (e.g. also lichen with cyanobacteria
as photobionts).
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