9.E. Non-Photochemical Quenching (NPQ) Protocol
The NPQ protocol is the most typically used measuring approach to quantify photochemical and non-
photochemical quenching. The measurement should be performed with a dark-adapted sample. Thereby,
it may not be appropriate under field conditions.
The NPQ protocol starts by giving a measuring light to acquire minimal level of fluorescence Fo. A short
saturating flash of light is then applied to reduce the plastoquinone pool and measure maximum
fluorescence in the dark adapted state, Fm. After a short dark relaxation, the sample is exposed to actinic
irradiance for tens to hundreds of seconds to elicit a transient of the Kautsky effect. Moreover, a sequence
of saturating flashes is applied on top of the actinic light to probe the non-photochemical quenching NPQ
and effective quantum yield of photosynthesis QY in light adapted state. After exposure to continuous
illumination, the relaxation of non-photochemical quenching is determined by means of saturating pulses
applied in dark.
Two NPQ protocols, NPQ1 and NPQ2 are predefined. The protocols differ in the duration of the light
exposure and the dark recovery phase, in the number and interval between pulses. See table below.
maximum fluorescence in dark-adapted state, measured during the first
saturation flash after dark adaptation
1
L - indicates light adapted parameters; D - refers to dark recovery phase after switching of the actinic
illumination; n - represents a sequential number of light phase; ss - steady state
2
Calculated as (Fm – Fo) / Fm
3
Calculated as (Fm_Ln – Ft_Ln) / Fm_Ln or of corresponding steady state or dark recovery parameters
4
Calculated as (Fm – Fm_Ln) / Fm_Ln or of corresponding ss, Dn or Dss parameters
5
Calculated as (Fm_Ln – Ft_Ln) / (Fm_Ln – Fo_Ln) or of corresponding ss, Dn or Dss parameters
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