Explanation

Biogeochemical cycles are broadly categorized into gaseous cycles and sedimentary cycles based on their primary reservoir pool:

– Phosphorus Cycle (Sedimentary): Phosphorus has no significant gaseous atmospheric phase. Its primary natural reservoir resides within the lithosphere in the form of phosphate rocks (apatite minerals). The natural weathering and erosion of these rocks dissolves inorganic phosphates into soils and waterways, making them bioavailable for uptake by terrestrial and aquatic plants.
– Carbon Cycle: The primary active reservoirs are the atmosphere and hydrosphere (dissolved CO₂).
– Nitrogen Cycle: Driven by the atmospheric pool, which contains roughly 78% elemental nitrogen gas that requires biological or industrial fixation.
– Sulphur Cycle: While partly sedimentary, the sulphur cycle features significant volatile gaseous phases (hydrogen sulfide, H₂S, and sulphur dioxide, SO₂) from volcanic and oceanic emissions.

Therefore, weathering of rocks is the fundamental release mechanism in the Phosphorus cycle — Option C.