GardenBanter.co.uk - View Single Post - How much plant biomass is needed per human?

[email protected] · 19-07-2007, 04:17 PM posted to sci.bio.botany

In article . com,
wrote:
How much plant biomass is needed per human?

In the first place, someone will (correctly) respond that the question
is poorly conceived, hopelessly vague, dependent on too many unknowns,
etc.

It's not the existing biomass, it's the ability to increase total biomass,
since plants only consume CO2 at a rate higher than they produce it when
they grow. Ideally, you could suck up and discard excess CO2 by growing
something like duckweed, and chucking it out the airlock.

Granted. Cleaning up the question will probably be the first step
towards finding a meaningful answer.

So let's start with these:
* I'm referring to O2 and CO2 exchange only; not using plants as
food, fuel, building materials, etc.
* We can all recognize that humans have varying needs. One size does
not fit all.
* The O2 output per gram of one plant is probably wildly different
than that of another species.

It's not just the species, it's the growing conditions. Light intensity,
duration and wavelength, water and humidity, character of the growing
medium, nutrients, toxic materials, temperature, and many other factors
(including CO2 and oxygen concentrations) all affect plant growth.

Asked another way:
Assume that one normal healthy adult human is placed in a sealed
environment with everything needed, except a renewable oxygen supply,
and he wants to live there indefinitely. How much plant life should
be included in this environment? (Ignore the fact that the artificial
environment will almost certainly degrade quickly due to other
causes.)

There has been a *lot* of work done on this, mainly in the glory days
of NASA when they had a big budget and funded research on closed systems
for manned space flight of long duration and self-sustaining orbital
colonies.

More recently, there was Biosphere II, which eventually failed for a
number of reasons, the most interesting of which was insufficient CO2.
The designers didn't take into account the slow but steady absorption
of CO2 by concrete during the first decades after it is poured.

Thank you!

Ted Shoemaker

P.S. No, this isn't a homework assignment. I'm just trying to learn.

It is an interesting question, and a lot of smart people have put a lot
of thought into it, not just scientists and engineers, but science fiction
writers and fans.