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Diurnal cycling

P.Ralph at uts.edu.au P.Ralph at uts.edu.au
Fri Apr 21 03:45:06 EST 1995

Can anyone on this listserver help me ?

Recently I completed several experiments to investigate the temporal effect
of the diurnal irradiance cycle on the photosynthesis of a species of
seagrass. I am using chlorophyll a fluorescence to monitor the condition of
PSII. One experiment was carried out on field collected specimens, and
produced a Fv/Fm curve with a midday trough and dawn and dusk maxima.  This
could be a photoprotective response to prevent excess irradiance during the
midday peak solar insolation.

However, when the experiment was run using cultured specimens from the same
location, the Fv/Fm curve was inverted, with a midday peak and dawn and
dusk minima.  The light was constant and the same as the plants had been
cultured at for 6 months prior to the experiment.

Why is the Fv/Fm curve now showing a midday peak, if it was simply
responding to the level of irradiance it should go straight to maxima and
remain there until the lights are turned off ?

Any suggestion, or ideas would be greatly appreciated.

Regards Peter

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