Photochemical and non-photochemical quenching coefficients of the chlorophyll fluorescence: comparison of variation and limits

There are several types of quenching coefficients currently in use which describe the decrease of the chlorophyll fluorescence: the photochemical quenching coefficients q(P) and q((P)rel) and the non-photochemical quenching coefficients q(N), q((N)rel) and NPQ. These five coefficients were calculated for a broad variety of cases of the fluorescence signals in a normal, realistic range and for determining the limits in a range with extremely low and high fluorescence values. The calculations showed that the quenching coefficients currently in use are not only numbers between 0 and 1 as one would expect when taking them as a relative measure of the quenching process. Most quenching coefficients must be regarded and interpreted carefully separated from each other. Each photochemical quenching coefficient and each nonphotochemical quenching coefficient describe the same fluorescence signal in a different way. Only the relative quenching coefficients q((P)rel) and q((N)rel) match together and can be used to demonstrate a shift of the energy de-excitation from the photochemical to the non-photochemical route.