Earth's atmosphere constitutes 78% of Nitrogen, then why do plants need to absorb Nitrogen from the soil. Why couldn't it possible for them to absorb the atmospheric Nitrogen like they do in the case of CO2.
Most of the plants relies on other sources to fix their Nitrogen, why couldn't be there a single plant which can absorb atmospheric Nitrogen ?
Is there any ancient plant which is considered to be using atmospheric Nitrogen ?
I have done a simple research, I could only find that previously atmosphere is not so abundant with Nitrogen and plants developed mechanisms to use Nitrogen fixed in soil. So now they are following the same mechanism when Nitrogen is abundant in the atmosphere. Is this a valid answer ?