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One of deficit resources on Mars is nitrogen. There's a plenty of carbon dioxide, and a modest amount of water. There's a deficit of nitrogen, but AFAIK plants use nitrogen in compounds found in soil, not from the atmosphere. This could be provided.

While long-term human habitation would likely necessitate atmosphere similar to Earth, would this be necessary for large biodomes? Could plants, given enough light and water, thrive in atmosphere of oxygen and carbon dioxide, without atmospheric nitrogen? Also importantly, could they live with reduced atmospheric pressure - so that the biodomes wouldn't need to withstand a whole 1bar differential, but say, 0.3 bar, similar to what was used in Apollo missions?

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    $\begingroup$ An atmosphere without nitrogen may oxidize some chemical compunds of the plants more frequently than on earth. Especially if the partial pressure of oxygen is greater than 0.2 bar. Some oils of the plants may be a fire risk in pure oxygen. A cloth damped with linseed oil may self ignite on earth if simply left alone for some hours. The oxidation of the oil heats up the cloth to glow and visible flames. $\endgroup$ – Uwe Feb 28 '17 at 14:37
  • $\begingroup$ @Uwe: Isn't partial pressure of oxygen on Earth at sea level about 0.2 bar? $\endgroup$ – SF. Feb 28 '17 at 14:54
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Despite the fact that on Earth, Nitrogen is the most abundant element in the atmosphere, plants do not get their nitrogen from the air - it is just too hard to get it. A plant would need to expend lots of energy to break the N2 bonds.

Instead, they get all their nitrogen from the soil, where bacteria in the soil have already converted N2 to NH3 (nitrogen fixation), and onwards to NH4, NO2 and NO3, which are much easier for plants to use.

So yes, as long as you could supply nitrogen in the soil, plants could thrive without nitrogen in the atmosphere.

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    $\begingroup$ There are some plants which gets their nitrogen from N2 in the soil. See en.wikipedia.org/wiki/Lupinus. The plants use a symbiosis with special bacteria to convert N2 to NH3. But the bacteria can't do it without the plant and also the plant can't do it without the bacteria. Only the bacteria has the necessary enzyme but the plant protects the enzyme against to much oxygen. $\endgroup$ – Uwe Feb 13 '17 at 20:34

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