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photosynthesis-latency period?

Edward Doran edoran at OCEAN.WASHINGTON.EDU
Mon Jul 10 11:03:36 EST 1995

	Sorry if this may look a little long, but it is such a cool subject...
On Thu, 6 Jul 1995, Karen Culver-Rymsza wrote:
> Of course with strong stratification you may have some indication of what
> the actual light levels of exposure may be, to a first approximation.
> (remember Beer's Law). If you have a strong layering of phytopankton, for
> example at the thermocline, you may be able to estimate the light field
> even better (but don't forget self-shading).
Absolutely. In this case you can characterize both the light field and 
exposure of the phytoplanktoners, so to a first approximation 
this is true. But I was also thinking that it is important to consider the 
history and trajectory of the planktoner to get an understanding of potential 
productivity.  For example, lets say there is strong stratification but 
the organism has a diurnal migration or was recently advected into the area 
(this would effect both its nutrient and photosynthetic characteristics).

> > One thing to think about though, is short term 
> > exposures to high light levels can result in photosynthetic rates that are 
> > higher than would be predicted from a standard P vs.I curve 
> This is comparable to results found for understory plants exposed to
> sunflecks, where it has been found that brief exposure to high light
> levels significantly increases photosynthetic yields and rates.

Perhaps another cool example would be the focusing and defocusing of 
light as surface waves pass overhead [overfrustule?;)]. 

> (so photosynthesis
> > varies with time, irradiance, and physiology). So the length of time you watch
> > after the "go!" and what you end up calling the maximum photosynthetic rate is
> > actually quite important.
> Yes but some idea of the time period for _acclimation_ to new light levels
> usually is given as around a generation time, which for most algae means on
> the order of a day or three.  However there are myriad shorter term mechanisms
> available to the cells to deal with short term changes in light, from the
> xanthophyll cycle to phosphorylation, but these are not considered
> photoacclimation in the true sense, but photoprotective.

I guess I think of most shorter time period adjustments as a "photoresponse" 
rather than strictly as a photoprotective mechanism.  For example, when a 
phytoplanktoner is mixed to depth (on short time scales) its encounter 
rate limits photosynthesis rather than its ability to process light 
energy.  There are a number of mechanisms that act on time scales 
similar to mixing regimes to deal with this without being 
necessarily photoprotective. 

> > 	My work is focused on studying how light regimes and 
> > perturbations interact with the molecular biology (gene expression, cell cycle
> > progression) of phytoplankton.
> Me too! but I am looking at the cell bio aspects of such things.  Which of
> course beg molecular biological questions as control mechanisms. 

GREAT!  Are there many phycologist out there?

> Hopefully helpful
> Karen Culver-Rymsza



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