Our atmosphere is on the order of 71% nitrogen, so why would they need the gum to saturate it further?
The same reason we have nitrogen fixing bacteria, it's not in a usable form for them to use.
Oh yeah, good point. Gaseous nitrogen is relatively inert, isn't it?
Yes, it takes bacteria in the soil to make it into a usable form, then plants take it to bring it into the food chain.
It's like Ask Science, but for all universes other than our own. Or as **fanlore.org** calls it [Watsonian point of view](http://fanlore.org/wiki/Watsonian_vs._Doylist)