What vegetation would thrive in the Martian atmosphere?

Question

Most plants require carbon dioxide for their photosynthesis, which Mars has in overabundance.

Would atmosphere composition (let's ignore temperatures for the purpose of this question) of Mars allow vegetation to grow?

Answer 1

This is not my field by a long shot, so take what I say with a grain of salt. However, this question is very hard to answer because whether or not a plant will grow depends on a great variety of factors. Even if we ignore the temperature as you say, there are other considerations. These include, but are not limited to:

• Soil composition, I doubt that Martian soil can support earth vegetation even if its atmosphere could. Plants need various nutrients, and specific pH ranges among other things.

• Atmospheric pressure, I am not at all sure that the Martian atmosphere (though it is, indeed rich in CO₂) would be enough to drive an earth plant's photosynthesis. Bear in mind that the atmospheric pressure on Mars averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure (source). This makes it highly unlikely that unmodified earth plants would be able to thrive there.

• Water water water...

• Pollinating species. Many many plants depend on other species (e.g. bees or hummingbirds) for their propagation. These would be hard to find on Mars.

• Sunlight I don't know if Mars receives enough sunlight at its distance from the sun to drive an unmodified plant's photosynthesis.

Now, that said, it should theoretically be possible to start with some extremophile archaea or bacteria that would over the course of many many many years (at least hundreds, thousands more probably) terraform Mars to make it suitable for human habitation. Specially engineered plants could play a role then but I find it very hard to believe that any existing, unmodified, multicellular plant life of earth origin could survive on Mars.

Answer 2

I'll stick to considering the atmospheric composition, as referred to in the original question: Although there may be some rare exceptions that I can't recall, under normal circumstances all green plants use aerobic respiration with O₂ as final electron acceptor for energy production. This means that they require oxygen, which is essentially absent from the Martian atmosphere (0.13%). Even though our hypothetical Martian crop could produce oxygen as a byproduct of photosynthesis, that oxygen would be lost into the atmosphere, and would not be available for respiration.

I believe that under waterlogged conditions some plants can switch temporarily to some sort of anaerobic metabolism as a stress response, but I don't know if this is just to survive or whether the plants can grow in this way - I suspect it is the former.