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Saturation pulse duration
Set up screen #1
Setting saturation pulse duration
Duration is the time that the saturation flash is turned on. For higher plants, times of 0.5
to 1.5 seconds have been used. The optimal saturation duration for algae and
cyanobacteria is between 25 and 50 msec. (Schreiber 1995). If the duration is not long
enough, then PSII is not fully saturated, even at the highest intensity, and Fm values are
reduced. If the Duration is too long, on most chlorophyll fluorometers, the saturation
pulse peak becomes subject to a type of NPQ that rounds the tailing edge of the
saturation peak and also reduces the average Fm value. The Ideal saturation pulse peak is
flat on the top with the trailing edge rounding minimized (Roseqvist and van Kooten
2006).The OS1p provides an automation feature that uses a rolling continuous eight point
average to find the highest average value on the top of the saturation pulse. These eight
points represent a time of 25 msec. As a result, the optimal saturation duration is
automatically provided for higher plants, algae and cyanobacteria if the duration is long
enough. 0.8 seconds is adequate for most plants. The saturation pulse duration is
adjustable between 0.1 and 2.0 seconds.
To adjust the duration, touch the upper right graphic display window of the quenching
measuring window, and then, touch the “Flash Width” button.
It is best to use the Y(II) protocol or the Fv/Fm protocol to test the correct width of the
saturation pulse because only one saturation pulse is displayed and it is magnified on the
trace screen. The width may be adjusted and viewed by touching the trace display screen
in these two protocols. Select the full view, adjust the width of the saturation pulse, until
the trace looks like the trace in the middle picture or the one on the right. If the saturation
pulse is too narrow, it does not matter how high the saturation flash is set, it will not fully
saturate PSII. If the saturation pulse is too wide, the automated optimal measuring routine
will still provide the optimal measurement. On other chlorophyll fluorometers, the
average Fm’ value is reduced by the curvature of the trailing edge of the saturation pulse
caused by a form of NPQ (Roseqvist and van Kooten 2006).
The saturation “Flash Width” may be set from 0.1 seconds
to two seconds. The flash width is commonly set between
0.5 seconds and 1.5 seconds for optimal work. The width
must be long enough to fully saturate PSII but narrow
enough to prevent saturation flash NPQ from reducing the
average value of Fm’, the saturation intensity value. 0.8
seconds is a good default setting for most plants, however,
if you would like to test your plant, use the following
method.
