The process illustrated by the downward arrows from the atmosphere showing the conversion of nitrogen gas (N₂) into usable forms available to producers is nitrogen fixation. Nitrogen fixation is the biological or chemical process that converts inert atmospheric nitrogen gas into ammonia (NH₃) or related compounds that plants can absorb and use. This process is primarily carried out by certain bacteria and archaea, including symbiotic bacteria like Rhizobium in legume roots, as well as free-living bacteria such as Azotobacter. The enzyme nitrogenase catalyzes this reaction by breaking the strong triple bond in N₂ and reducing it to ammonia, which can then be incorporated into organic molecules by producers (plants) for growth and development
. In summary, the downward arrows represent nitrogen fixation-the transformation of atmospheric nitrogen into a biologically usable form for producers in the ecosystem
