Abstract

Although dinitrogen (N2) gas represents almost 80% of the Earth’s atmosphere, it is not a source of nitrogen (N) that is readily available to plants. However, a number of procaryotic microorganisms have evolved that utilize the enzyme nitrogenase to reduce atmospheric N2 to ammonia, which can subsequently be used to support their growth. Biological N2 fixation (BNF) by some diazotrophs can occur in a free-living state, or via associative relationships with plants, while others can fix N2 only in symbiosis with specific plant hosts.