Nitrogen cycle, simple explanation of how it works. Practical example of how atmospheric nitrogen ends up in the human food chain.
To understand the importance ofnitrogen cycleI'll explain what it is starting from an anthropocentric point of view.
L'nitrogenit is essential for the survival of us human beings. L'nitrogenit serves for the production of vital compounds such as amino acids (proteins) and nitrogenous bases (nucleic acids). The largest nitrogen reserve on earth is the atmosphere where nitrogen occupies about 78% of the total volume. Nitrogen in the atmosphere is not the most useful for us humans because it cannot be absorbed by plants.
To play a fundamental role in the nitrogen cycle they are in fact the plants. A small part of nitrogen is found in the soil and plants manage toassimilate nitrogenthrough absorption by the root system.
This is why it is important to fertilize plants with manure, compost or other compounds with a high nitrogen content! Just think that, in optimal conditions, the corn plants grown in one hectare of land are able toabsorb and fix 450 kg of nitrogenin a year!
In the pots we have on the balcony, the earth pigs contribute to the nitrogen cycle by behaving like real scavengers!
Nitrogen cycle, simple explanation
Plants absorb nitrogen through various compounds present in the soil (nitrates, nitrites and ammonium salts). Once absorbed and organized by plants, nitrogen serves to increase the plant mass.
From plants, nitrogen is transferred to animal organisms through the food chain: we humans are omnivores, we feed on livestock that is fed by plant-based feed (rich in nitrogen) and we feed on the same plant mass (fruit and vegetables) .
The decomposition of the organic remains in the soil (the same decaying vegetable debris, animal carcasses, faeces, secondary products of metabolism ...) enriches the soil with nitrogen. From the ground, nitrogen can return to the atmosphere also thanks to some specialized bacteria.
Even if I explained thenitrogen cycle in a simple way, let's talk about acycleextremely complex.
Nitrogen passes from the atmosphere to the ground through fixation. Fixation is a chemical process (reduction) by which the molecular nitrogen present in the atmosphere (N.2) is first transformed into ammonia (NH3) by fixing bacteria such as Azotobacter and Clostridium, but also by cyanobacteria and rhizobia, bacteria that live in symbiosis with the roots of some plants such as legumes.
Nitrogen is found in the soil mainly due to the decomposition of organic nitrogen. Nitrogen is present in grass, in pruning cuttings and in any organic residue in the form of nitrogenous bases (DNA) and amino acids (proteins). So the decomposing bacteria do nothing butdecompose organic matterand release nitrogen in the soil. The nitrogen will then be reabsorbed by the plants again, sending the so-calledcycle.
Molecular nitrogen is found in the soil with different oxidation numbers and absorbed by plants mainly as nitrate, but also as nitrite or ammonia.
The biological fixation of nitrogen is essential for agriculture and for the growth of the plant mass.
How do plants absorb nitrogen
Plants take up nitrogen as ammonium or nitrate ions. In plants, a process known asnitrogen organization. That is, nitrogen is bound to organic molecules. Thus the nitrogen moves in a smallcycleformed by plants, animals and bacteria. Although overall, as seen, the nitrogen cycle starts from the atmospheric one: part of the nitric nitrogen is in fact transformed by specific denitrifying bacteria which then release the nitrogen into the atmosphere in the form of molecular nitrogen.
Specifically, the plants are able to absorb nitrogen because at the level of the plant cells of the root system there are specific transporters that operate asimportbetweennitrateisprotons(H + found dissolved in the ground).
Nitrate, in the plant cell, is processed by an enzyme known as"Nitrate reductase"which operates the transformation of nitrate to nitrite. Subsequently, the nitrite is further reduced to ammonium ion and it is at this point that nitrogen organization can take place. Only when nitrogen (entered in the form of nitrate) is converted to ammonium (passing through nitrite) will the incorporation of nitrogen into vital molecules such as proteins and nucleic acids take place. Then the food chain does the rest!
Composting is one of many examples of nitrogen cycle. For further information:composting, how it works.
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