Phosphorus Cycle

Life is a complex interplay of matter and energy. All life on Earth ultimately derives its energy from the Sun. The Sun is a star that bombards our planet with solar radiation. It is a nearly inexhaustible source of light energy for the living organisms that inhabit the earth. As abundant as this energy source is, however, there is a finite quantity of matter, or chemical elements, available to make up living things. Therefore, life on Earth, because it depends both on energy and matter, must depend on the reclaiming of materials for use over and over again. Essential nutrient elements are recycled between living and abiotic components of ecosystems in biogeochemical cycles, or cycles involving living (bio-), geological (geo-), and chemical processes. When living things die, they return their chemical elements to the non-living components of ecosystems as they decompose. However, even while alive, organisms contribute to nutrient cycling as they consume matter and excrete waste products into the environment.

There are several major biogeochemical cycles rotating continuously within and among ecosystems. An ecosystem is an area including all of the living and nonliving things found within it. The most important cycles of ecosystems are the carbon cycle, the nitrogen cycle, the phosphorus cycle, and the water cycle. These interacting biogeochemical cycles involve travel of carbon, nitrogen, phosphorus, and water through living things, air, water, soil, and rock. For instance, the carbon cycle involves the gas carbon dioxide found in air. Plants use carbon dioxide during photosynthesis to make plant material, like cellulose. Here, carbon moves from an inorganic gaseous form, to living, or organic, form. Then, as plants die, they decompose and release organic molecules into water, which then runs into oceans. The organic material settles to the bottom where, over very long time periods, is incorporated into rock. Thus, the carbon existed as a gas in air, living material in plants, dissolved matter in water, and as solid form in rock. In much the same way, phosphorus is recycled in the environment. Not every cycle, however, includes each of these stages.