opti-sciences OS1p - Cookbook Checklist before Making y(II) Measurements

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As with the “Fv/Fm” test, far-red pre-illumination is an option. Far –red illumination may
also be turned off or turned on during the entire measurement. If ambient sun light is used
for yield measurement, far-red light is provided by sunlight. It can be added in the set up
menu if internal artificial illumination is used to drive PSI . Internal actinic illuminators
filter out far red light.
When the test is triggered, Fs (or F’) the measure of steady state fluorescence is
determined and then the saturation pulse is applied to close all capable PSII reaction
centers for determination of Fms (or Fm’). In steady state photosynthesis, Fms is
depressed from Fm by non-photochemical quenching,
The resultant data is then processed to find Yield Y(II), (or )F/Fm’). A graph of the
measured data is displayed along with measured and calculated parameters. ETR or
relative electron transport rate and leaf temperature are also displayed if the measurement
is made with a PAR clip. PAR Clips are optional accessories.
“Default” PAR values can be put in the measuring file as well as measured values. This
is done on the Yield test calculations screen. “Default” PAR is an estimate of actual PAR
values.
When the optional PAR Clip is not used, this number sets the PAR reading. It has a range
from 0 to 2496 uE in steps of 1 uE (1 uml), and it allows estimated ETR. If the PAR Clip
is used, then the measured PAR value is always automatically reported to the measuring
file.
Cookbook checklist before making Y(II) measurements.
Fm’ is maximum fluorescence in a light adapted environment at steady state
photosynthesis. Fs’ is the fluorescence signal in a light adapted environment at steady
state photosynthesis.
Y(II) is = (Fm’ – Fs’) / Fm’ = )F/Fm’
1. Leaves must be at steady state photosynthesis. This takes between fifteen and
twenty minutes at a new light level. Above canopy leaves on a clear day, in the field, are
considered to be at steady state photosynthesis. (Maxwell and Johnson 2000).
2. It is dangerous to make Y(II) measurements on below canopy leaves in the field.
The shade from higher leaves and wind can interrupt a plant’s adjustment to steady state.
The xanthophylls cycle, and )ph of the thylakoid lumen adjust in about four minutes
although it takes longer in the field. (Lichtenthaler 2004) State Transitions take between
fifteen and twenty minutes to completely adjust. State transitions are a big factor at lower
light intensities, but they are not much of a factor at high light intensities. Rapid light
curves and Fv/Fm may be better solutions for below canopy work where appropriate.