99
For a more in depth discussion on this topic, see Quantum photosynthetic yield of PSII –
an in depth discussion of its value and limitations in chapter one.
“PAR Corr” is for correcting PAR sensor location error according to Rascher (2000).
When some artificial light sources are used, Rascher found that the location the PAR
sensor relative to the leaf surface can cause an error of up to 10%. This error is
insignificant if sun light is used due to the much greater distance from the light source.
Rascher used an independent PAR sensor and measured the intensity at the leaf plane. He
then made corrections due to PAR Clip sensor location, by comparing the differences
between the PAR clip values, and the leaf plane values. This correction may not be
needed for most relative comparison ETR applications, however it has been made
available for more exacting work when necessary.
Notes: When using the blue modulated light it was found that the average absorption
value should be set to 0.94 instead of 0.84 as is used by the red modulated light.
By plotting ETR vs. PAR, potential ETR rates, photosynthetic capacity, and ETR rate
limitations, at given light intensities, can be determined. (U. Schreiber 2004). Note: Four
electrons must be transported for every CO
2
molecule assimilated or O
2
molecule
evolved.
It has been found that Rapid Light Curves are a better solution in a variable light
environment. Light saturation rate, as measured by rapid light curves, highly correlates
with the concentration and maximum activity of Rubisco (Macintyre 1997), (Macintyre
1996). Measured Steady state photosynthetic rates overestimate actual photosynthetic
rates in a variable light environment (Macintyre 1997).
Error messages common to the test modes:
There are several common errors that can occur in the test modes.
If the battery voltage is 10.5 or less, the warning message “!! Battery Low !!” will appear
and a long beep will be sounded.
If the amount of in-band IR radiation is above set limits thereby saturating the pre-
detector the error message “!! IR to High !!” will be displayed.
“Fluorescent signal too low” appears if there is not enough signal getting to the detector.
This may be due to the fiber optic being too far from the sample, the intensity of the
modulated source being too low or the gain control is set too low.
“FL > 3600 pos det pin out” appears if the combination of the modulated light intensity
and modulated light gain are set too high. To fix the problem go to Auto Gain on the
setup screen, put a leaf in the PAR Clip, and press Auto Gain. The modulation intensity
will adjust automatically.
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