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Multi-flash vs. standard single flash saturation pulse
Multi-flash (“Step Int Lin Regr”) -
measuring yield at high actinic light levels.
The multi-flash option has been added to correct for the inability of very intense
saturation light pulses to completely close reaction centers under high actinic light
conditions. It is thought to be caused by mechanisms responsible for non-photochemical
quenching. Research has found that under high actinic light conditions, measured
electron transport rates (ETR) and yield values did not correlate well with carbon
assimilation measurements. The inability of very intense light saturation pulses, of any
intensity, to close all reaction centers, was thought to be the culprit.
By using multiple saturation light pulses of varying intensity, and linear regression
analysis, an infinite saturation pulse intensity can be estimated. It was found by Earl
(2004) that by using multiple intense saturation pulses at varying intensity levels, one
could use regression analysis to estimate the intensity of an infinite saturation pulse.
Testing was done on corn (C
4
plants), and on cotton plants (C
3
plants) and it was found
that in non-photo-respiratory conditions, the linear relationship between ETR and gross
CO
2
assimilation was restored by using the Fm’ or saturation pulse correction method.
This option should be considered for yield and ETR measurements when actinic light
levels are high. When used, The Fm’ value displayed on the graphic screen represents
Fm’ at infinity. The R
2
value is also displayed on the graphic screen. Saturation pulse
intensities used in the multi-flash mode are preset at the factory. When used with a PAR
Clip, they are at 2,133
:
mols, 4,400
:
mols, and 6,000
:
mols. The total flash duration that
includes all three values is 1.0 second.
Since the Earl work, Bernard Genty the man that developed quantum photosynthetic
Yield of PSII, back in 1989, has co-authored a poster that supports the work of Earl and
the use of regression analysis for correction of yield and ETR values. A Licor research
team of team of Loriaux S.D., R.A Burns, Welles J.M., McDermitt D.K. that also
included Bernard Genty of Cadarache DEVM-Laboratoire d’Ecophysiologie
Moleculaire des Plantes of the University of Marseille, studied the issue. They found that
in Z. mays, with the standard saturation pulse method, in high light field conditions,
measurements produced up to a -41% error in ETR values, and up to a -22% error in
Y(II) values . The research recommends the Multi-phase flash process for field
measuring work. The research is titled “Determination of Maximal Chlorophyll
Fluorescence Using A Multiphase Single Flash of Sub-Saturating Intensity”. (Loriaux
S.D., R.A Burns, Welles J.M., McDermitt D.K. Genty B. (2006) “Determination of
Maximal Chlorophyll Fluorescence Using A Multiphase Single Flash of Sub-Saturating
Intensity”. Abstract # P13011 August 1996. American Society of Plant Biologists Annual
Meetings, Boston MA).
