Neoformed aluminosilicate and phytogenic silica are competitive sinks in the silicon soil–plant cycle

[Display omitted] •Plant available silicon (Si) primarily depends on the weatherable minerals reserve.•Mineral dissolution releases Si flowing into two sinks: allophane and phytolith.•Allophanic and phytogenic Si reservoirs are being built simultaneously.•Allophane rapidly neoformed at a maximum rate of 0.85 g allophane kg−1 soil day−1.•The contribution of soil phytoliths to plant Si increases with weathering stage. In soils, mineral weathering and phytolith dissolution release aqueous monosilicic acid that can be taken up by plant, adsorbed on mineral surfaces, entrapped in neoformed clay minerals, or exported to watersheds. The balance between biotic and abiotic processes determines the fluxes of bioavailable silicon (Si), impacting plant growth and health, and diatoms biomass, hence the oceanic capacity to fix carbon dioxide. Here we quantified this balance in an experimental system using rice and an albic soil material (quartz grains) containing no weatherable silicate minerals. Materials representing a soil weathering gradient were prepared by adding variable amounts of silicate minerals within fresh powdered tephrite (