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In forest ecosystems, the silicon (Si) mass-balance at the watershed scale can be strongly influenced by readily soluble Si components, such as dissolved Si, adsorbed Si, amorphous silica (biogenic and pedogenic opal) and short-range ordered aluminosilicates. The aim of the present study is to (a) identify the components of the readily soluble Si pool in the Cambisol found below three tree species, under homogeneous soil and climate conditions, and (b) study the impact of Si recycling by tree species on the Si pools. We therefore measured the concentrations of Si extracted by Na₂CO₃ (Si_alk), oxalate (Si_ox) and CaCl₂. The Si_alk concentration decreased from the humus layer to 15 cm depth and then slightly increased until a depth of 75 cm. In the humus layer, the Si_alk concentration consisted mainly of phytoliths and differed significantly between tree species (expressed as mg SiO₂ g^-1): Douglas fir (14 …