Nitrogen fixation is performed anaerobically by the Nitrogenase part, and aerobically by the Nitrogen-Fixing Plastid.
Nitrogen fixation is the process of producing ammonia from atmospheric nitrogen and ATP, and in the case of aerobic Nitrogen Fixation, oxygen as well. Make sure that the gasses you need are present in your location before using this process. It is also important to consider the required ATP cost.
Use and Strategy
Nitrogen fixation is available in two different forms, with the basic anaerobic fixation being available to both prokaryotes and eukaryotes, while the eukaryote exclusive aerobic fixation is more efficient but requires the addition of oxygen in it's process. Nitrogen Fixation allows you to save time searching for ammonia by allowing you to produce it yourself, leaving you to only really have to worry about phosphates. If you find yourself with excess ATP generation, nitrogen fixation is an excellent way to make use of it.
This prokaryotic part takes up a single hex in size, and produces a small amount of ammonia. If there is no oxygen available, this part may actually be more viable than it's eukaryotic cousin since it does not require oxygen to function.
This eukaryotic part occupies two hexes of space, and produces much more ammonia than it's prokaryotic predecessor as long as sufficient oxygen is present in the environment. Due to it's reliance on oxygen, nitrogenase may be the better option if you find yourself somewhere lacking oxygen.
Function in Reality