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Re: Plants DO respire in light

On Tue, 7 Sep 1999, Tom Barr wrote:

> >>> Lighting on 24/7 won't give the best results either. Plants/algae
> >>> have to respire too!
> > There seems to be a common misconception that plants synthesize in
> >light, then respire in darkness.
> Thanks for pointing this out. All life, except namely some bacteria and
> other organisms, respires aerobically (at least in active cells) 24hrs a day
> whether photosynthesis is taking place or not.

And of course, there are the important qualifiers.  Some plants (C4
plants) perform part of their photosynthesis in the light, then store the
results and complete the rest of the process at night.  With 24/7 lighting
those plants will die.

Also I recall from John Raven's book "Transport and energetics in aquatic
plants" that respiration rates in the light are usually lower than in the
dark. Some plants may drop their respiration rates in the light to as
little as 5% of their respiration rate in the dark.  Apparently the
variation lets them divert resources like ADP/ATP to photosynthesis during
the day, and back to respiration at night.  Plants that use large
day/night swings in their respiration rates will probably fail if they
don't get dark periods.

Roger Miller