Biology · Ch 14 — Ecosystems and Energy Flow
Phosphorus Cycle
Phosphorus Cycle
The phosphorus cycle is the cyclic movement of phosphorus through the hydrosphere, lithosphere and biosphere. Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy-transfer systems, and many animals additionally require large quantities of it to build shells, bones, hooves and teeth.
The natural reservoir of phosphorus is rock, where it occurs in the form of phosphates. When rocks are weathered, minute amounts of these phosphates dissolve into the soil solution and are absorbed by plant roots; herbivores and other animals then obtain phosphorus by consuming plants. When organisms die or produce waste, phosphate-solubilizing bacteria decompose this material, releasing phosphorus back into the soil. Unlike the carbon cycle, the phosphorus cycle has no respiratory release into the atmosphere at all, since phosphorus has no significant gaseous phase. …
What this figure shows. A cyclical diagram showing how phosphorus moves between rock, soil, living organisms and sediment without an atmospheric gas phase. Phosphate locked in rock is released by weathering and geological uplifting, dissolving into the soil solution, from where plant roots absorb it. Animals obtain phosphorus by consuming plants, and decomposers break down the waste products and remains of plants and animals, returning phosphate to the soil. Some dissolved phosphate is carried away from the soil by rainfall, leaching and surface runoff into water bodies, where detritus settles to the bottom and, over long geological timescales, sedimentation converts this material back into new phosphate-bearing rock — clos …