[extropy-chat] Nuke 'em

Damien Sullivan phoenix at ugcs.caltech.edu
Sun Oct 23 19:13:07 UTC 2005

On Sun, Oct 23, 2005 at 11:25:40AM -0700, Robert J. Bradbury wrote:

> > "Clearly plants are really inefficient and we can do better!"  But I
> > suspect the limiting factor is the low concentration of CO2; dealing with
> > a 300 ppm input can't be pretty.
> I think that may only be a small part of the problem.  For land plants
> like corn and vegetables, the problem is lack of complete coverage
> (sunlight on soil doesn't help much).  Sugarcane and wheat are better
> in this respect.  Part of the problem is incomplete absorption of the solar
> energy.  Plants should *not* be green.  They should be black.  Obviously

A while back I read _Why Big Fierce Animals Are Rare_ by Paul Colinvaux, an
ecologist.  IIRC he said something like most plants get 8% in their growth
phase under optimal conditions.  They're all using the same chloroplasts,
after all.  Algae are just always in the growth phase.

More to the point, he said plants' energy efficiency in dim light is often
much higher, such as 20%.  This could be "evolved assuming shade" but could
also be a sign that energy isn't the limiting factor.  And here's a question:
to make a plant growing at high noon grow faster, do you increase the
intensity of light, or increase its CO2 concentration?

And what are the thermodynamics of getting CO2 from 300 ppm to 100,000 ppm or
whatever the C concentration in biomass would be?

> they are losing the energy in the green photons (which is significant).

OTOH, we might expect on evolutionary grounds that if most photosynthesizers
aren't using all the photons then there isn't much gain for them to do so.

> Ultimately the problem is that the standard photosynthetic harvesting
> apparatus is not using the full energy of each photon.  Its delivering

Which is why a solar heat engine can produce electricity better than a
photovoltaic, at least in direct light.

> If you study the light absorption frequencies of various photoplankton
> you will discover they are very precisely tuned for the light energy
> which reaches the water depth they inhabit.  Land plants are not so clever.

Any references to read more in?

-xx- Damien X-) 

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