know the phosphorus cycle: Definition, role and, Cycle
know the phosphorus cycle: Definition, role and, Cycle After getting to know the various cycles, this time we will learn about the phosphorus cycle. The phosphorus cycle may not be very commonly discussed, but phosphorus still plays an important role in our lives both directly and indirectly. Phosphorus is a nutrient that is quite limited for biological productivity in the terrestrial environment. The presence of the element Phosphorus is also very limited in the ecosystem. This is due to the slow rate of soil weathering and the limited release of phosphorus by ecosystem productivity [1].
Phosphorus plays an important role for all forms of life including the preparation of genetic material such as DNA and RNA, energy transfer (ATP and ADP), and the formation of certain organ structures supported by membranes (phospholipids). In organisms that carry out photosynthesis, phosphorus is used as an essential nutrient that can build their tissues with the help of solar energy [2]. Phosphorus in bedrock, soil, and sediment cannot be utilized directly by organisms. Phosphorus that has not been utilized will be converted into a dissolved orthophosphate form that can be assimilated through geochemical and biochemical processes in the global phosphorus cycle. The activity of microorganisms in the soil and sediment will affect the concentration and chemical form of phosphorus in it [2].
The phosphorus cycle globally or as a whole consists of several stages, each of which also has a cycle. The phosphorus cycle begins with the phosphorus cycle on land, phosphorus transport from rivers to the sea, and the phosphorus cycle in the oceans. We need to know that the contribution of phosphorus in nature today is the result of a mixture of human activities (not completely naturally occurring). Phosphorus was originally derived from the mineral apatite which was then dissolved through chemical and physical weathering processes [1]. The form of phosphorus commonly found in nature is the phosphate ion. Phosphate ions can be found in sedimentary rocks, volcanic ash, aerosols, and mineral dust [3].
Phosphorus Cycle on Mainland
In the phosphorus cycle that occurs on land, the phosphorus content in the soil does not only occur naturally, but there is also a contribution from human activities such as fertilization. The exchange of phosphorus between the biota and the soil takes place very quickly compared to the exchange of phosphorus that only exists in the soil. The phosphorus content in the soil generally comes from weathering of the apatite mineral [1].
Phosphorus in the soil is also produced from mineral grains through several processes such as a decrease in pH levels resulting from things related to respiration and organic acids released by plant roots. The decrease in pH levels resulting from respiration takes place around the root hairs which dissolve phosphorus-containing minerals (the mineral apatite) and release phosphorus into the root pore spaces. The release of organic acids by tree roots can also dissolve apatite minerals and release phosphorus into the soil pores [1].
Phosphorus has the characteristics of being very immobile or immobile and the rate of diffusion of its solubility is very slow from its dissolved form. Thus, phosphorus will be difficult to absorb by the roots and reach the soil surface. However, phosphorus in the soil is still in the form of organic matter which cannot be directly used by plants. Therefore, plants have certain ways to be able to utilize phosphorus. The first way is with the phosphatase enzyme, where this enzyme can release inorganic phosphorus that is available naturally from organic matter. Generally, this enzyme is excreted by plants, microorganisms in the soil, and in symbiosis with the Mycorrhizal fungus which can cover the small roots of plants and help to excrete the phosphatase enzyme. Another way is to use organic acids to release phosphorus and provide an active site so that phosphorus can diffuse rapidly from the soil pores to the root surface [1].
The presence of phosphorus in the soil is available in various forms and changes can occur rapidly over time and soil development. Forms found in the soil can be classified into refractory (not bioavailable) and labile (biologically available). Refractory forms include apatite and precipitated phosphorus minerals which are adsorbed into iron or magnesium oxide hydroxide. As for the unstable forms such as dissolved phosphate ions (located in the soil pores) and nonoccluded phosphorus which are on the soil surface. The presence of phosphorus in the soil can be reduced or lost if there is a runoff that carries phosphorus to rivers through water [1].
Phosphorus Transport from River to Sea
Phosphorus carried from land to sea is generally carried by river water first. Phosphorus in rivers comes from weathering rocks on land and soil. Phosphorus in rivers is generally associated with particulate matter because phosphorus is reactive to particles [2]. The presence of phosphorus in rivers is in two forms, namely particulate and dissolved. A river that continues to flow and empties into the ocean, will carry phosphorus from the land as well as from the river itself to the open sea [1].
Phosphorus Cycle in the Ocean
Phosphorus that reaches the ocean will enter the marine ecosystem system including the food webs in it. When it enters the ocean, phosphorus in the form of phosphate will be taken up by phytoplankton as an important component for photosystems and their cells. Photosystems are a way to utilize phosphate as the basis for the formation of ATP and ADP as well as energy transfer. At the cellular level, phosphorus is also used to form cell walls which are composed of phospholipids . When phosphate is not available in the ocean or the level is too low, the organisms in it will take advantage of its complex form and convert it into orthophosphate through enzymatic reactions and microorganisms .
After knowing the phosphorus cycle in each stage, we can understand that the phosphorus that is in nature today is not really derived from the natural cycle but there is also a human contribution in it. Agricultural activities that use fertilizers with phosphorus content in them can increase phosphorus levels in the soil to the ocean. However, it should be noted that excessive phosphorus content in aquatic ecosystems will cause eutrophication.
Eutrophication is a phenomenon where there is a very dramatic growth of algae, so that light and oxygen will be difficult to penetrate through the surface of the water. This can be dangerous for other biota that live in it because it will lack nutrients and experience hypoxia (lack of oxygen to breathe). The impact is that there will be mass death of the biota that live in it. Therefore, the balance of phosphorus in land and water is very important to maintain the balance of the ecosystem