What is the lowest pressure at which plants can survive? How the plants behave in a Martian-type atmosphere? Is there any plant that can survive such atmosphere?
Can a lichen grow at Martian pressure?
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Low surface pressure on Mars (averaging 600 Pa or about 1/170 of Earth's at sea level) is only one difficulty that an organism would have to contend with. In addition, mean surface temperatures are ~210 K (- 63 °C), the surface ultraviolet flux is extremely high (no ozone layer) and an aridity comparable to the Atacama desert. On the plus side, a 95% CO2 atmosphere might promote photosynthesis.
So, higher plants are extremely unlikely to prosper on Mars. Purely in terms of pressure, experiments suggest that at 1/10 Earth atmospheric pressure vascular plant transpiration increases significantly. So much so that they enter into a drought response which often leads to plant death.
However, lichens may be another matter. These are often adapted to low precipitation/pressure environments such as high mountains. Indeed, this article addresses exactly your question (sadly it is not open access). The authors suggest that the lichen Xanthoria elegans experiences no loss in vitality after 22 days exposure to laboratory Mars-like conditions (low pressure, low temperature etc.)!
Having skimmed this article I am frankly amazed (and slightly dubious) at the result. However, it should be noted that they only ran the experiment for 22 days, applied no ionising radiation (to simulate the high UV flux) and make little mention of the precise metabolic state of the lichen. If it has entered into cryptobiosis (cessation of metabolic processes) then it can't exactly be regarded as prospering.
Short answer : around 0.47 atm
World's highest plants discovered growing 6 km above sea level
It does seem that some of Earth’s toughest life could survive on Mars.
Neither of those are plants though.
Cyanobacteria are bacteria.
lichens are a composite organism incorporating a fungus & algae or cyanobacteria.
Algae are plants, but it's in a lichen, not a standalone plant, it's not clear from the article any of those lichens were algal rather than ones with cyanobacteria either.
But (that bit of pedantry aside) it would seem the answer to your second question is yes.
A lichen can grow at Martian pressure.
So there are examples of life that clearly can survive lower pressures than 0.47 atm.
But actual plants don't seem to be among them.
No, the lowest pressure at which plants can survive is not around 0.47 atm.
It is 0.07 atm or less in the case of ryegrass. And it's the total pressure. Not partial pressure of one of the constituent gases.
See this article: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860010460.pdf
... almost 8 years later..
A newer experiment with a timespan of 1.5 years on another one lichen species suggests that there is
.. a minor resistance potential of the lichen Buellia frigida towards Low Earth Orbit and Mars analogue conditions effecting the survival potential and the resistance of the symbiotic organism
due to a DNA damage.
Source: "DNA damage of the lichen Buellia frigida after 1.5 years in space using Randomly Amplified Polymorphic DNA (RAPD) technique" Backhaus et al, 2019 Planetary and Space Science
So the answer is possibly "no" until we find some Martian lichen.