How is phosphorus cycled in terrestrial and marine ecosystems?

Phosphorus is cycled in ecosystems through weathering, absorption by plants, consumption by animals, and decomposition.

Phosphorus, unlike other nutrients such as nitrogen and carbon, does not have a gaseous phase and its cycle is primarily confined to the lithosphere and oceans. The phosphorus cycle begins with the weathering or erosion of rocks, releasing phosphate ions and other minerals into the soil and water bodies. This process is slow and often the limiting factor in ecosystem productivity as phosphorus is a vital component of DNA, RNA, ATP and phospholipids - essential for life.

In terrestrial ecosystems, plants absorb these phosphate ions from the soil through their roots. The phosphorus is then used in the formation of organic compounds necessary for plant growth. Animals obtain phosphorus by consuming these plants or by eating other animals that have consumed the plants. When plants and animals die, their bodies, wastes, and any unused phosphorus are broken down by decomposers like bacteria and fungi. This returns the phosphorus back into the soil where it can be used again by plants. Some of the phosphorus also leaches into groundwater and is carried into rivers and eventually into the ocean.

In marine ecosystems, the phosphorus cycle is more complex. Phosphorus enters the ocean from rivers and becomes part of the ocean sediments. Some of it is used by marine organisms for their metabolic processes. When these organisms die, they sink to the ocean floor where they are decomposed, returning the phosphorus to the sediment. Over time, geological uplift can bring these ocean sediments back to the land surface where weathering can occur again, thus completing the cycle.

Human activities such as mining and the use of phosphorus-rich fertilisers can significantly alter the phosphorus cycle. These activities increase the rate of phosphorus input into ecosystems, which can lead to an overabundance of phosphorus, causing problems such as eutrophication in water bodies. Understanding the phosphorus cycle is therefore crucial for managing and maintaining the health of both terrestrial and marine ecosystems.