@MiniStoj Well I dug up my academic credentials and searched for hours but couldn’t get easy access to the full paper. All I got was the abstract. ::shoulders slumped:: I did find like 20 articles I have been wanting to read though so that’s nice. ::perks up::
So seeing as I have no idea what literature you actually looked at… I figured you might like to look at this article, which explores exactly what you were talking about:
Wehkamp, C.A. et al. Radish (Raphanus sativa L. cv. Cherry Bomb II) Growth, Net Carbon Exchange Rate, and Transpiration at Decreased Atmospheric Pressure and / or Oxygen. Gravitational and Space Biology Volume 26 (1). April 2012.
In the study, they grew radishes at various reduced pressures. Partial pressure of CO2 was maintained at 120 Pa, and they then varied pO2 and total pressure. Changes in total pressure had almost no effect, but they got down to 7 kPa pO2 before starting to just barely see some growth loss. When they dropped down to 2 kPa pO2, root dry mass dropped to about 15% of normal, and harvest index (% edible portion) plummeted from ~65% to ~24%.
So from this, we can pretty reasonably expect to be able to have a “growth chamber” with as little as 7% of normal atmospheric pressure, provided that most of that is O2. On the other hand, since people will still need to work inside the chamber, a 21 kPa pO2 environment is probably better.
For water, the max vapor pressure at growth chamber temperatures is about 3-6 kPa. It’s pretty common for chambers to be at 70-100% humidity, so we can expect to see almost maximum pressure from water.
Now I’ve done some research on CO2 toxicity in plants, and apparently it varies pretty widely between species (and even within cultivars of the same species). The cut off I hear most people talk about before symptoms start is usually around 500-1000 Pa (which is about where toxic effects start to occur in humans also). Did you find higher thresholds?
All told, I’d say we can expect about 3 kPa from water vapor, at most 1 kPa from CO2, and the rest should be O2. With the total pressure being either 10-11 kPa or 23 kPa depending on if you want to have people in there for things like pruning and what not. With the right crop (like radishes), you could probably just plant and harvest without any human involvement. Does that align with what you found?