87Sr/86Sr 及δ88/86Sr被廣泛用於風化作用的示蹤計。植物位於岩石-大氣-水圈的交界，深受其各交互作用影響，且於研究中指出植物在攝取元素時，會增加周圍風化的速率。但植物造成之87Sr/86Sr分化因過於微小而被忽略。近年來因δ88/86Sr各領域研究應用的蓬勃發展，植物被指出會造成顯著δ88/86Sr分化，顯示其對於風化研究的重要性，但植物與環境間更詳細的交互作用關係，比如在植物體內造成的δ88/86Sr分化，則仍未被詳細研究。本研究欲利用empirical external normalization搭配standard-sample bracketing修正法，修正使用多接收器感應耦合電漿質譜儀量測鍶同位素時所造成的質量偏移，並研究在白楊樹利用鍶元素時所造成之δ88/86Sr同位素分化，並協助我們了解植物在整體鍶循環中所扮演的角色，進一步建立更完整的鍶的源匯模型。在白楊樹中造成δ88/86Sr分化的過程主要有三階段，分別為：根部攝取鍶元素時造成之分化、鍶自根部運輸至莖部時所造成之分化、鍶自莖部運輸至葉的過程中造成之分化。利用公式計算之平均白楊樹δ88/86Sr為-0.18‰，明顯較生長土壤(δ88/86Sr =0.02‰)富集86Sr。根據瑞利分鎦模型模擬出之白楊樹連續取用鍶造成之同位素分化影響，則顯示當白楊樹移除所有溶於水中的鍶元素時，可造成土壤溶液中達2.99‰分化。此模擬結果可再次強調植物為一富集86Sr的儲藏庫，並且在鍶源匯模型中扮演不可或缺的角色。

Triple Strontium (Sr) isotopes have been extensively applied as tracers for weathering processes in the terrestrial environments. Plants located on the of rock-water-soil interface, and have been known to accelerate the weathering rate when they mobilizes metals from soils. Recent studies showed plants may play a non-negligible role in the biogeochemical cycle of strontium using the δ88/86Sr, but the relationship between plants and the environments were still unclear. Here we aim to use δ88/86Sr to demonstrate how plants affect the δ88/86Sr in soil, even evaluate the plant influence to the chemical weathering process in forest systems. The poplar trees that cultivated at the Swiss Federal Research Institute for four months were chosen for the experiments. We used an empirical external normalization (EEN) combined with standard-sample bracketing (SSB) procedures to correct the potential mass drifting during Sr isotopes measurements on multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) . The results allow to identify a three-step Sr isotopic fractionation levels in poplar trees. The first one takes place when Sr entering the root. The second one takes place as Sr transported from root to stems, followed during the Sr translocation from stem to leaves, and δ88/86Sr decreased with height. The average poplar δ88/86Sr value (-0.18‰) showed enrichment of 86Sr compare to the soil solution (δ88/86Sr =0.02‰). According to an estimation using Rayleigh fraction model, poplar trees can produce significant δ88/86Sr fractionation in water which up to 2.99‰ if all the dissolved Sr was removed by the poplar trees. This supported the vegetation is the lighter 86Sr reservoir and likely plays an important role in Sr cycling in terrestrial environments.

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