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Re: CO2 use at night

In response to the original question from Steve Pushak...

> Mark wrote:
> >CO2 is used directly by plants; there is no chemical precursor or
> >storage product for CO2.

And Eric wrote:

> This is probably true in all aquatics but not all plants.  Many desert
> plants employ a system in which CO2 is taken up by the plant at night and
> temporarily fixed into a storage molecule (not ribulose).  Upon sunrise,
> the plant shuts its pores up tightly, thereby preventing water loss in the
> heat.  CO2 that has been stored up during the cool night is then released
> from the storage molecule and dropped in the calvin cycle as
> photosynthesis provides ATP and NADPH.  At night the plant opens up
> for gas exchange once again.  I don't remeber the detailed biochemistry
> but I think these plants are called CAM plants.

"CAM" stands for Crassularian Acid Metabolism, and is typical of
succulents and cacti.  Oddly, there are aquatic succulents.  Crassularia
aquatica comes to mind.

Raven discusses both C4 metabolism and CAM as means for aquatic plants and
algae to conserve CO2 and compete for limited CO2 supplies.  In the case
of CAM, the plant could take up CO2 at night when there is less
competition for a limited CO2 supply and use it during the day when light
is available but CO2 is not.

I don't recall if Raven documented CAM in any aquatic plant, but he
certainly argued (at length) that they should exist.

> Water not being a major concern for aquatic plants <g> I don't think that
> this comes into play in our systems, and so I apologise for straying into
> the "Off Topic Zone".  Just wanted to set the biological record straight.
> - -Eric

See?  You weren't as off-topic as you thought!

Roger Miller