photosynthesis--latency period?

Karen Culver-Rymsza kculver at GSOSUN1.GSO.URI.EDU
Sat Jul 8 10:12:33 EST 1995



On Wed, 5 Jul 1995, Edward Doran wrote:

> Howdy,
> 	Well it may depend on the length of time after the "go!" that you 
> want. There has been quite a bit of debate, given the hydrography of the 
> water mass and the physiology of phytoplankton, when if ever (in some cases) 
> they reach steady state.

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).

> 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.

(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.

> 	In the interest of full disclosure I'll tell you that I am only a 
> graduate student.  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. 

Hopefully helpful
Karen Culver-Rymsza



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