『Abstract
　The quantification of silicon (Si) uptake by tree species is a mandatory step to study the role of forest vegetations in the global cycle of Si. Forest tree species can impact the hydrological output of dissolved Si (DSi) through root induced weathering of silicates but also through Si uptake and restitution via litterfall. Here, monospecific stands of Douglas fir, Norway spruce, Black pine, European beech and oak established in identical soil and climate conditions were used to quantify Si uptake, immobilization and restitution. We measured the Si contents in various compartments of the soil-tree system and we further studied the impact of the recycling of Si by forest trees on the DSi pool. Si is mainly accumulated in leaves and needles in comparison with other tree compartments (branches, stembark and stemwood). The immobilization of Si in tree biomass represents less than 15％ of the total Si uptake. Annual Si uptake by oak and European beech stands is 18.5 and 23.3 kg ha^-1 year^-1, respectively. Black pine has a very low annual Si uptake (2.3 kg ha^-1 year^-1) in comparison with Douglas fir (30.6 kg ha^-1 year^-1) and Norway spruce (43.5 kg ha^-1 year^-1). The recycling of Si by forest trees plays a major role in the continental Si cycle since tree species greatly influence the uptake and restitution of Si. Moreover, we remark that the annual tree uptake is negatively correlated with the annual DSi output at 60 cm depth. The land-ocean fluxes of DSi are certainly influenced by geochemical processes such as weathering of primary minerals and formation of secondary minerals but also by biological processes such as root uptake.

Keywords: Phytolith; Silicon cycle; Temperate forest; Tree species』

Introduction
Materials and methods
　Experimental site
　Materials
　　Tree compartments
　　Forest floor horizons
　　Soil organo-mineral and mineral layers
　　Solutions
　Biomass evaluation
　Analytical methods
　　Si contents in tree compartments
　　Si contents in organic horizons
　　Si content in organo-mineral and mineral layers
　　Si content in solutions
　　Microscopic analysis
　　Determination of Al and Ti contents in selected samples
　Statistical analyses
Results
　Si contents in the various compartments of the soil-tree system
　　Tree parts
　　Organic horizons and soil layers
　　Solutions
　BSi and ASi particles morphologies
　Total Al and Ti content in the selected samples
Discussion
　Si uptake by forest trees
　DSi output
　Origin of Si in organic horizons
　Budget of Si in the soil-tree system
　Implications
Conclusion
Acknowledgements
References