Question

Explain phosphorus cycle and draw a simple diagram of this cycle in a terrestrial ecosystem.

Answer 1

Phosphorus cycle (sedimentary cycle):

1. Reservoir: Rocks and natural phosphate deposits in the lithosphere.
2. Weathering: Phosphate is released from rocks and deposits into the soil as orthophosphate \[\mathrm{PO}_{4}^{3-}\].
3. Uptake: Plant roots absorb phosphate, helped by mycorrhizae.
4. Transfer: Phosphorus moves to animals through food.
5. Decomposition: Dead matter and excreta return phosphorus to the soil. Phosphatising bacteria convert organic phosphorus into phosphate.
6. Loss: Phosphate combined with iron, aluminium or calcium becomes insoluble and settles in deep ocean sediments. Phosphate in bones and teeth also remains locked for long periods.

The phosphorus cycle is slow and sedimentary, with the rock reservoir as its main source.