Nitrogen fixation

The atmospheric nitrogen needs to be processed through nitrogen fixation for it to be useful to plants. Nitrogen fixation can occur with lightning strikes but most often it’s caused by symbiotic bacteria or the free living bacteria. Nitrogenase enzymes from these bacteria combine with the N2 gas with Hydrogen in order to produce the ammonia which is then being converted to the organic compounds. Rhizobium is one example of these bacteria and they live in the roots of legumes like beans or peas. They are in a mutual relationship with the legumes where they produce the needed ammonia while they are receiving carbohydrates from the plants. Soils that are deficient in nutrients can regain the nutrients by planting legumes on them to increase the nitrogen. Few plants can do this too. Now, 30% of the fixed nitrogen is being manufactured by chemical plants for ammonia.

Conversion of N2

The conversion of the gas nitrogen from the atmosphere to a form that is readily available to plans is important for animals and humans as it’s an important step for the nitrogen cycle that distributes the essential nutrient. There are 4 ways to convert the atmospheric nitrogen gas to more reactive chemical forms. First is the biological fixation. Symbiotic bacteria most often found on legumes and some other free-living bacteria cn fix the nitrogen to be organic nitrogen. Rhizobium bacteria is one example of this type of bacteria and they live in the root of legume nodules. They are diazotrophs. Free-living bacteria example is the Azotobacter.

At 600 degrees centigrade and with iron as a catalyst, the atmospheric nitrogen combined with hydrogen from petroleum or natural gas, at really high pressure would be turned to ammonia or NH3. Explosives and fertilizers use the Haber-Bosch process of converting the gaseous nitrogen and hydrogen to NH3. Fossil fuel combustion release NOx. There are other processes that could form NO from the Nitrogen and Oxygen from the atmosphere such as the photons caused by lightning.

Assimilation

There are plants that absorb nitrogen from the soil in the form of ammonium or nitrate ions. Nitrogen obtained by animals and humans can be traced to the foods they eat. Plants have root hairs that absorb the ammonium or the nitrate ions from the soil. Nitrate is firstly reduced to nitrite ions then to ammonium ions to be incorporated into amino acids, chlorophyll and nucleic acids. Plants that have a mutual relationship with the rhizobia bacteria, some of the nitrogen is absorbed as ammonium ions from the nodules directly. Animals, heterotrophic organisms and fungi are able to absorb nitrogen in the form of amino acids, small organic molecules or as nucleotides.

Ammonification

Ammonification is the process wherein the organic form of nitrogen is turned to ammonium ion again. This happens when an animal or plant dies or from their expelled waste. Enzymes that are involved in this process are GS or Gln Synthetase, GOGAT, and GDH.

Nitrification

Ammonium conversion to nitrate is primarily performed by the soil-living bacteria as well as other nitrifying bacteria. The first stage is the oxidation of the ammonium ion that is performed by these bacteria like the Nitrosomonas that converts the ammonium to NO2 ions. Nitrobacter and other species of bacteria then convert nitrites to nitrates. This is important because too much of the nitrite ions are already toxic to plants.

Denitrification

The denitrification process reduces the nitrates to the inert nitrogen gas again and this is what completes the nitrogen cycle. Pseudomonas and the Clostridium bacteria are in charge of this process in an anaerobic condition. They use the nitrate in place of the oxygen for respiration as an electron acceptor.