Nitrogen is one of the most abundant and most important elements in biological systems. To sustain all living systems requires a source or sources of combined nitrogen (nitrogen in combination with other elements. The degree of importance and metabolic costs of such combined nitrogen to biological systems is highlighted by the extent and sophistication of the regulatory systems which have evolved to obtain and manipulate nitrogen compounds in all biological systems.
All higher plants obtain nearly all of their nitrogen in one of 3 combined forms, either as NO3-, as NH4+, or as urea. In an agricultural context this combined nitrogen is derived from basically three sources. It is either mined from the ground (principally as nitrate salts); it is produced chemically from elemental nitrogen and hydrogen by the Bosch-Haber Process (ammonia); or it is produced by biological nitrogen fixation processes involving a number of microorganisms which are either free living or grow in symbioses with higher plants.
The supply of nitrate salts for mining is limited, and the production of NH3+ by the Bosch-Haber process requires extremely high temperatures and pressures generated at the expense of fossil fuels. Consequently, two considerations have created interest in replacing chemically fixed nitrogen with biologically fixed nitrogen. First, the energy costs required to generate the high temperatures and pressures required have forced chemically fixed nitrogen costs continually higher to the point that the cost of nitrogen fertilizer has become a significant production costs. And second, the fossil fuel input leads to concerns over the sustainability of agricultural systems requiring nitrogen inputs. The view is generally held that improving the processes of biological nitrogen fixation can diminish both of these concerns.
23.01. Organisms that Fix N
23.02. Nitrogenase
23.03. Structure of the Nitrogenase Complex
23.04. Reductants Used for Biological Nitrogen fixation
23.05. Protection of Nitrogenase from Oxygen Damage
23.06. Hydrogen Production and Nitrogenase Efficiency|Nitrogen Fixation|Organisms that Fix N|Nitrogenase|Structure of the Nitrogenase Complex|Reductants Used for Biological|Nitrogen fixation|Protection of Nitrogenase from Oxygen Damage|Hydrogen Production and Nitrogenase Efficiency|
