We explain what the phosphorus cycle is, its stages and importance for life. In addition, in which cases this cycle is altered.
What is the phosphorus cycle?
The phosphorus cycle or phosphoric cycle is the circuit that describes the movement of this chemical element within a given ecosystem . Phosphorus (P) is a non-metallic , multivalent, highly reactive element , which is found in nature in various inorganic rock sediments , and in the body of living beings , in which it is a vital part although on a small scale.
The phosphorus cycle is part of the biogeochemical cycles , in which life and inorganic elements maintain a balance so that various chemical elements are recycled and reused. This cycle would not be possible in rapid terms without the trophic chains of the different ecosystems .
However, compared to the cycles of nitrogen, carbon or water , it is an extremely slow cycle, since phosphorus does not form volatile compounds that can easily move from water to the atmosphere and from there back to the land, where it originates from.
Plants also play a vital role in the fixation and transmission of phosphorus, as will be seen when we analyze their different stages.
Importance of the phosphorus cycle
Phosphorus is an abundant element in terrestrial minerals. Although it plays an indispensable role in living beings , it is little present in the body of living beings. It is part of the most important macromolecules, such as DNA , RNA or ATP (Adenosine triphosphate).
Consequently, it is essential for obtaining energy at the biochemical level , as well as for the replication of life and hereditary transmission. In this way, the phosphorus cycle is essential for life as we know it.
Stages of the phosphorus cycle
We can study the phosphorus cycle in the following stages:
- Erosion and weathering . Phosphorus abounds in terrestrial minerals, which are found on land or at the bottom of the seas. The continuing effects of rain, wind and solar erosion and accidental action of mining the human being , allow these phosphorus reserves to surface and be transported to the various ecosystems.
- Fixation in plants and transmission to animals . Plants absorb phosphorus from soils and fix it in their body, both in the case of terrestrial plants, as well as algae and phytoplankton that absorb it from marine waters. From there it is transmitted to the animals that feed on the plants, in whose bodies it is also stored, and in the same way to the predators of these herbivorous animals and to the predators of these, distributed along the trophic chain.
- Return to soil by decomposition . The excretions of animals are rich in organic compounds that, when decomposed by bacteria and other natural recycling organisms , return to be phosphates that can be used by plants, or transmissible to the soil. The same happens when animals die and decompose, or when the carrion left behind is broken down: phosphates return to the ground to be harnessed by plants or to continue draining in rivers and rains to the sea.
- Return to the ground by sedimentation . Another way of returning the phosphorus from the body of the animals to the earth, where it becomes part of sedimentary minerals, is much longer than that allowed by the animals, and has to do with the fossilization of their organic remains and the tectonic displacement of phosphorus reserves of organic origin towards the depths of the earth. But such geological surveys can take thousands of years to occur.
Alterations in the phosphorus cycle
The phosphorus cycle can be greatly altered by human intromissions. On the one hand, the release of phosphorus by mining action can increase the presence of this material on the earth’s surface , since its extraction by erosive natural roads would have taken thousands of years more.
On the other hand, the action of fertilizers used in agriculture , whether of natural or artificial origin, involves the injection into the soil of many more phosphates than it would normally receive. Such excess is washed by rain or irrigation waters, draining into water reservoirs, rivers or the sea.
The increase in phosphates and nitrogen also increases the algae and microorganisms that take advantage of it (a process called eutrophication ). Thus the trophic dynamics are unbalanced and algae often compete with each other until they die massively on the shore. When decomposing they generate pollution, and also increase the amounts of phosphorus circulating in seawater.