Diurnal cycling

Harald Teicher hteicher at biobase.dk
Wed May 3 06:12:42 EST 1995


P.Ralph at uts.edu.au wrote:

: 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



light is only one of the factors involved in photoinhibition, so you should 
also check that temperature, temp. fluctuations, salinity (assuming sea 
grass grows near the ocean), humidity (stomatal opening) are replicated in 
your controlled experiments

as i am also interested in the photoprotective response i would appreciate
your letting me know of any other responses you might receive 

harry




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