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This is a sealed room to only grow plants. I will be introducing C02 @ 1500 PPM to maximize growth, and I do not want to ventilate the room and loose my C02. So, I will have to introduce oxygen to the room. I know that we have about 21% in our atmosphere but I do not know what the Oxygen level needs to be in order to grow healthy plants?

This is the last thing I will need to know to finish my set up, everything else is in place and ready for plants.

I hope that you can find an answer for me as I have not been very successful on my own.

Thank you
Question Date: 2011-09-09
Answer 1:

Interesting question - it depends on what you're trying to study.

The value that matters in terms of biology is what is called partial pressure: the pressure exerted by the molecules of a gas in the absence of other gasses. So, for example, because our atmosphere is 21% oxygen, the partial pressure of oxygen in our atmosphere is 0.21 atmospheres. If you were to, say, double the atmospheric pressure inside of your greenhouse by adding whatever gas, you would still want 0.21 atmospheres of partial pressure of oxygen to simulate sea level conditions.

Now, you won't be doing that - 1500 ppm CO2 is 0.15 % CO2 by concentration, or 0.0015 atmospheres partial pressure. Your total pressure in your greenhouse will still be one atmosphere (approximately), so you're already good there.

Also keep in mind that adding CO2 will only help if CO2 is the limiting resource for your plants. This is almost never the case: plants are limited by water, nitrogen, phosphorous, etc.

Last, note that plants do fine at least somewhat lower O2 concentrations. High in the Sierra Nevada, for example, the entire atmosphere is thinner, so the partial pressure of O2 is going to be lower.

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