Is Your Fm′ Accurate?

Accurate measurements of light-adapted maximum fluorescence yield (Fm′) are essential for studies of many biophysical and physiological aspects of photosynthesis. Errors in estimates of Fm′ propagate through calculations of other parameters.

An innovative technique known as Multiphase Flash™ fluorescence quickly calculates the true Fm′ from a single flash event. This value, known as extrapolated maximum fluorescence yield (EFm′), is an accurate assessment of Fm′ at infinite irradiance contrary to traditional measurements of apparent maximum fluorescence yield (AFm′).

Experimental research shows that EFm′ values are invariably higher than
AFm′ values measured using saturating pulses of light (Q′)
(Figure 1). In some instances Fm′ differences can result in ΦPSII differences of as much as 15-30%.

The measured value of AFm′ increases with increasing Q′, whereas EFm′ measured across the same range of Q′ intensities is constant except at the lowest Q′.

Application Page:

chlorophyll fluorescenceChlorophyll

Application Note:
Stressed Plants?

Since this technique measures Fm′ using moderate flash intensities, plants that are sensitive to photodamage can be studied with less risk of damage from the flash.

Tradition flash method versus LI-COR's Multiphase Flash Protocol

Figure 1. Estimates of EFm′ and AFm′ as a function of saturation pulse irradiance (Q′) in chamber-grown Nicotiana tobacum.

Learn more about Multiphase Flash™ Fluorescence in this recent publication in Plant, Cell & Environment.

Learn more about 6400-40 Leaf Chamber Fluorometer


Scroll to Top