Magnesium retention on the soil exchange complex controlling Mg isotope variations in soils, soil solutions and vegetation in volcanic soils, Iceland
Magnesium retention on the soil exchange complex controlling Mg isotope variations in soils, soil solutions and vegetation in volcanic soils, Iceland
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DOI：
10.1016/j.gca.2013.09.036
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发表时间：
2014-01
影响因子：
5
通讯作者：
S. Opfergelt;K. Burton;R. B. Georg;A. West;R. Guicharnaud;B. Sigfússon;C. Siebert;S. Gíslason;A. Halliday
中科院分区：
文献类型：
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作者：
S. Opfergelt;K. Burton;R. B. Georg;A. West;R. Guicharnaud;B. Sigfússon;C. Siebert;S. Gíslason;A. Halliday
了解镁的生物地球化学循环不仅对陆地生态学至关重要，因为它是植物的关键营养元素，而且对于量化镁的化学风化通量和相关的大气二氧化碳消耗也是至关重要的，这需要区分生物和非生物对输出到水圈的镁通量的贡献。本文报道了冰岛五种火山土的母质玄武岩、土壤整体、粘粒、交换性镁、季节性土壤溶液和植被的镁同位素组成，以加深对控制镁向植被供应和向水圈输出的来源和过程的认识。散体土壤(δ26 mg/L=−0.40±0.11‰)与母质玄武岩(δ26 mg/L=−0.31‰)的同位素相似，而粘粒(δ26 mg/L=−0.62±0.12‰)、交换性镁(δ26 mg/L=−0.75±0.14‰)和土壤溶液(δ26 mg/L=−0.89±0.16‰)的同位素都比玄武岩轻。这些成分可以通过土壤交换复合体上的混合和同位素分馏过程来解释。重镁同位素的连续吸附-解吸导致重镁优先从土壤剖面流失，使土壤具有相对于母质玄武岩的轻镁同位素组成。此外，海洋喷雾和有机质分解的外部贡献导致了土壤交换复合体上镁来源的混合。植被优先吸收土壤交换复合体中的重镁(Δ2 6‰-exch=0.5 0±0.0 9‰)，植被中δ2 6 mg的变化反映了土壤中生物有效镁来源的变化。这项研究强调了在控制土壤和土壤溶液中镁同位素变化的因素中，镁在土壤交换复合体中的主要作用，并表明镁同位素为监测植物可利用并输出到水圈的镁的生物和非生物贡献提供了一个有价值的工具。
Understanding the biogeochemical cycle of magnesium (Mg) is not only crucial for terrestrial ecology, as this element is a key nutrient for plants, but also for quantifying chemical weathering fluxes of Mg and associated atmospheric CO2consumption, requiring distinction of biotic from abiotic contributions to Mg fluxes exported to the hydrosphere. Here, Mg isotope compositions are reported for parent basalt, bulk soils, clay fractions, exchangeable Mg, seasonal soil solutions, and vegetation for five types of volcanic soils in Iceland in order to improve the understanding of sources and processes controlling Mg supply to vegetation and export to the hydrosphere. Bulk soils (δ26Mg = −0.40 ± 0.11‰) are isotopically similar to the parent basalt (δ26Mg = −0.31‰), whereas clay fractions (δ26Mg = −0.62 ± 0.12‰), exchangeable Mg (δ26Mg = −0.75 ± 0.14‰), and soil solutions (δ26Mg = −0.89 ± 0.16‰) are all isotopically lighter than the basalt. These compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex. Successive adsorption–desorption of heavy Mg isotopes leads to the preferential loss of heavy Mg from the soil profile, leaving soils with light Mg isotope compositions relative to the parent basalt. Additionally, external contributions from sea spray and organic matter decomposition result in a mixture of Mg sources on the soil exchange complex. Vegetation preferentially takes up heavy Mg from the soil exchange complex (Δ26Mgplant-exch= +0.50 ± 0.09‰), and changes in δ26Mg in vegetation reflect changes in bioavailable Mg sources in soils. This study highlights the major role of Mg retention on the soil exchange complex amongst the factors controlling Mg isotope variations in soils and soil solutions, and demonstrates that Mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of Mg that is bioavailable for plants and is exported to the hydrosphere.