『Abstract
　Thorough characterization of the Si isotopic composition of the terrestrial biogenic pool could potentially allow Si isotope information to be used when assessing the relative contributions from biogenic and mineral sources to soil water, plants and surface waters. In the present study, the Si isotopic compositions of major biomass components in a boreal forest in Northern Sweden were investigated, along with the relative contributions from exogenous Si incorporated in the plant structure. This was achieved using chemical purification and high-resolution multi-collector inductively coupled mass spectrometry (MC-ICP-MS) for the precise and accurate determination of the Si isotopic composition of plants. The technique, which relies on multi-elemental analysis of plant ashes and sample-specific HF-dissolution followed by strong-anion exchange chromatography, allows efficient separation of Si from matrix and interfering elements, while recovering in excess of 99％ Si. The long-term instrumental reproducibility, expressed as two standard deviations (2σ), for the isotopic reference material NBS28 (n=12) was 0.06‰ for δ²⁹Si and 0.12‰ for δ³⁰Si. Results for the analyses of composite plant samples for the eight most prolific species in the boreal forest yielded a surprisingly homogeneous Si isotopic composition, expressed as δ²⁹Si (±expanded combined uncertainty) and δ³⁰Si, ranging from (-0.15±0.11)‰ to (0.13±0.06)‰ and (-0.31±0.08)‰ to (0.22±0.13)‰, respectively. Isotopic and elemental analyses of local airborne particulate material suggest that the exogenous Si contribution varies between ＜1％ and ＞70％, indicating that the potential surface contribution must be considered during Si uptake studies. The present study thus provides evidence that thorough appreciation of the forms of Si in plants is an absolute requirement when assessing the plant impact on the Si cycle via the difference in dissolution kinetics for phytoliths and lithogenic Si.

Keywords: Silicon isotopic composition; Plants; Phytoliths; MC-ICP-MS』

1. Introduction
2. experimental section
　2.1. Sampling site
　2.2. Samples and sampling
　2.3. Reagents
　2.4. Instrumentation
　2.5. Sample preparation procedures
　　2.5.1. Ashing procedure
　　2.5.2. Major element determination
　　2.5.3. Dissolution of biological ashes
　　2.5.4. Silicon separation using anion-exchange chromatography
　2.6. Mass spectrometric measurement
3. Result and discussion
　3.1. Silicon recovery and elution profile
　3.2. Blank contribution
　3.3. Elemental compositions of the plant materials
　　3.3.1. Major element concentrations and ash content
　　3.3.2. Using lichen Si/Al to correct for potential exogenous Si contribution
　3.4. Silicon isotopic composition of boreal forest vegetation
　　3.4.1. δ²⁹Si and δ²⁹Si values obtained during the analysis of bulk plant material
　　3.4.2. Presence of Si-containing exogenous material in boreal forest vegetation
　　3.4.3. Seasonal variations in the Si isotopic composition of lyme grass
　　3.4.4. Potential application of the Si isotopic composition of boreal forest vegetation
4. Conclusion
Acknowledgements
References