OT: Carbon Dioxide races -> known vs unknown -> terraforming mars -> is or is not

[dogscoff]

Sorry to double post, but I have a mostly on-topic question for my own sci-fi writing purposes, and this post has nothing to do with my Last.

I know Mars has a thin CO2 atmosphere. If we were to build a domed ecosystem on Mars, I imagine we could use photosynthesis or some chemical process to extract all the oxygen we needed from this CO2.

However, as has already been stated in this thread, our own atmosphere is mostly nitrogen, and that is also important to us. (Nitrates in the soil for plants etc)

Does anyone know if there is any useful amount of nitrogen present in the martian atmosphere, or is it all CO2? If there is none, would we be able to extract the required nitrogen from other nearby resources (rocks, asteroids etc)?

Finally, would an artificial atmosphere made up in this way (say ~75% nitrogen, ~15% oxygen, ~10% CO2) be viable for a human ecosystem, or would we need to import/ locally source all the other trace elements in our own atmosphere?