But can they reproduce in the soil at the same range of air pressure found in habitats, with the same gravity / gas mixture? Can they still reproduce after 50 years?
Despite a lifetime of 6-9 years, though, their generation length is only a few months; if they reproduce in that radiation environment for a year or three and there aren't serious mutations, they'll probably be okay in the long run.
Edit: Plants and non-human animals wouldn’t appreciate Martian rads either.
In any event, what you'd probably do is use reflected light to filter out high energy particles.
[1] We don't actually know how to make it work. The Biosphere 2 project was a spectacular failure, and it operated with a much less difficult set of constraints.
The risk of that life snuffing out may be small, but the time cost of replacement should that happen is huge.
The atmospheric pressure on the ISS is very close to 1 atmosphere, and it's an oxygen-nitrogen mix close to earth's atmosphere.
The issue is that the inert nitrogen has a really important role in carrying away heat from the flame. Fire is a dynamic reaction where temperature and speed is determined basically by how much heat a set of reagents produce/how much heat is carried away in the waste products. Nitrogen doesn't participate in the chemical reaction, but it gets heated alongside the waste gases, and so it reduces the temperature of the fire.
In a pure 0.2bar oxygen atmosphere, anything that would smoulder or burn slowly in standard atmosphere burn rapidly with a bright flame instead, and some things that you'd normally not consider flammable can sustain flame.
This is the reason the space station maintains a normal atmosphere instead of a thin pure oxygen one.
Conversely, if you double the amount of nitrogen (without reducing the amount of oxygen) in the air, almost nothing burns anymore.