Experiments studying the extent of different quenching changes under a series of light intensities require a 30-min dark-adaptation of leaf to get the Fv/Fm value, which represents the relaxed state of the leaf. But it's really time-consuming to conduct when there are multiple groups to measure. Then would it be reasonable to replace this value by the maximum Fv/Fm obtained at predawn when the plants are fully relaxed? And wouldn't the Fv/Fm from predawn be better since it excludes the impact of all the potential factors that possibly reduce the Fv/Fm during the diurnal time?
Hi,
As you say, the overnight-dark adaptation is usually available. Generally, 30 minute-dark treatment is not sure to be enough for dark adaptation, though it is usually enough. When you have to distinguish the NPQ and the photoinhibition, it is necessary to find the appropriate duration of dark treatment.
I think it will always be nice idea for scientific writing, using the overnight-dark treatment, to describe how many hours the plant samples were kept in the dark.
Ming-Wei Zhong There are many reports about Fv/Fm measured predawn. Some recommended only this way.
For instance, look at : Tomaszewski, Timothy, and Herman Sievering. "Canopy uptake of atmospheric N deposition at a conifer forest: Part II-response of chlorophyll fluorescence and gas exchange parameters." Tellus B: Chemical and Physical Meteorology 59.3 (2007): 493-501.
Fv/Fm ratio depends upon the proton flux (in general term light intensity). If the proton flux in predawn condition is nearly 0.1 to 0.01 micro mole/m^2 sec then fv/fm value in both dark adopted and predawn condition will be same and maximum.
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