How did plants evolve?

Why didn't plants evolve to fix nitrogen from the air and let bacteria fix carbon from the soil?

• I understand that plants pull carbon out of the air and bacteria fixes nitrogen from the soil for plants, but why isn't it the other way around? There is an abundant percent of Nitrogen in the atmosphere and an abundant percent of carbon in the soil probably due to this process, but if those percentages aren't a result of this symbiotic relationship between plant and bacteria, and if those percentages are inherent to the Earth itself, will plants evolve to pull the much needed Nitrogen out of the atmosphere and abandon carbon fixation to bacteria?

• Answer:

  * The carbon in the soil is less accessible not being water soluble. * Fixing nitrogen is ultimately exothermic so it can take place without total energy input.. * Reduction of CO2 is endothermic so sunlight energy input is required.