There are actually a bunch of plants that can pull N2 directly from air, by entering into a more direct symbiosis with nitrogen fixing bacteria in root nodules.

There are actually a bunch of plants that can pull N2 directly from air, by entering into a more direct symbiosis with nitrogen fixing bacteria in root nodules. (not typically trees though) Depending on where you live, you might even plausibly have some in your garden. https://en.wikipedia.org/wiki/Root_nodule https://en.wikipedia.org/wiki/Root_nodule