Fo
– Represents emission by excited chlorophyll a molecules in the antennae structure of Photosystem II. The true
Fo
level is only observed when the first stable electron acceptor of Photosystem II called
Qa
is fully oxidised. This requires thorough dark adaptation.
Fv
– Indicates the variable component of the recording and relates to the maximum capacity for photochemical quenching. Calculated by subtracting
Fo
value from the
Fm
value (
Fm - Fo
).
Fv/Fm
– An indication of the maximum quantum efficiency of Photosystem II and widely considered to be a sensitive indicator of plant photosynthetic performance. Presented as a ratio between 0 and 1, healthy samples typically achieve a maximum
Fv/Fm
value of approx. 0.85. Values lower than this will be observed if a sample has been exposed to some type of biotic or abiotic stress factor which has reduced the capacity for photochemical quenching within PSII. is presented as a ratio of variable fluorescence (
Fv
) over the maximum fluorescence value (
Fm
) and is calculated as (
Fm - Fo)/Fv
.