『（Abstract）
　Silicon has a crucial role in many biogeochemical processes - for example, as a nutrient for marine and terrestrial biota, in buffering soil acidification and in the regulation of atmospheric carbon dioxide. Traditionally, silica fluxes to soil solutions and stream waters are thought to be controlled by the weathering and subsequent dissolution of silicate minerals^1,2. Rates of mineral dissolution can be enhanced by biological processes³. But plants also take up considerable quantities of silica from soil solution, which is recycled into soil from falling litter in a separate soil-plant silica cycle that can be significant in comparison with weathering input and hydrologic output^4-8. Here we analyse soil water in basaltic soils across the Hawaiian islands to assess the relative contributions of weathering and biogenic silica cycling by using the distinct signatures of the two processes in germanium/silicon ratios. Our data imply that most of the silica released to Hawaiian stream water has passed through the biogenic silica pool, whereas direct mineral-water reactions account for a smaller fraction of the stream silica flux. We expect that other systems exhibiting strong Si depletion of the mineral soils and/or high Si uptake rates by biomass will also have strong biological control on silica cycling and export.』

（Text）
Methods
　Water samples
　Phytolith extraction
（References）
Acknowledgements

Figure 1: Plot of Ge/Si against [Si] from Hawaiian stream waters. Data are from ref. 12 and this study. The hyperbolic curve is a two-component mixing model, in which component 1 is derived from the dissolution of biogenic silica and has Ge/Si = 0.25×10-6 and [Si] = 1,800 μM, and component 2 is derived from the dissolution of soil minerals and has Ge/Si = 2.6×10-6 and [Si] = 25 μM. Hawaiian streams generally show lower [Si] and higher Ge/Si at high discharge. The discharge-weighted stream fluxes have Ge/Si ＜ 1 and [Si] ＞ 80 μM, implying that component 1 is the larger contributor of dissolved silica and indicating a major role for biogenic silica in controlling stream Si export. Labelled crosses on the mixing curve indicate the modelled fraction of biogenic Si. 〔Derry,L.A., Kurtz,A.C., Ziegler,K. and Chadwick,O.A.(2005): Biological control of terrestrial silica cycling and export fluxes to watersheds. Nature, 433, 728-731.から〕 成分�@：Biogenic Silica（phytolith-derived Si） Ge/Si＝0.25×10-6および [Si]＝1,800 μM 成分�A：Soil minerals（weathering-derived Si） Ge/Si＝2.6×10-6および [Si]＝ 25 μM.

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