Black Jay R, Epstein Emanuel, Rains William D, Yin Qing-Zhu, Casey William H
Department of Geology, University of California, One Shield Avenue, Davis, California 95616, USA.
Environ Sci Technol. 2008 Nov 1;42(21):7831-6. doi: 10.1021/es8012722.
Magnesium is an essential nutrient, which activates more enzymes than any other mineral element and, thus, plays an important role in biogeochemical cycles. With three stable isotopes naturally abundant (24Mg, 78.992%; 25Mg, 10.003%; 26Mg, 11.005%), magnesium stable isotope fractionation may provide insights into these cycles. Here, we detail for the first time the magnesium stable-isotope distribution in a higher plant, wheat (Triticum aestivum L.), during its growth cycle. Wheat plants were grown in a limiting nutrient supply hydroponically, some being left to mature through senescence and others detopped at maturity for collection of exudates. Measurements of the magnesium isotopic composition of chlorophylls, seeds, shoots, roots, leaves, exudates, and the limiting nutrient solution over time show that the plant appears to establish an isotopic equilibrium with the nutrient available to it and that the plant (in particular, the seeds and exudates) becomes enriched in the heavy isotopes of magnesium in a mass-dependent relationship as the plant reaches maturity. The preference of the plants for heavy magnesium isotopes suggests that a difference might exist in the bioavailable magnesium of agricultural and natural soils due to the periodic removal of heavy magnesium isotopes by harvest.
镁是一种必需营养素，它能激活比其他任何矿质元素更多的酶，因此在生物地球化学循环中发挥着重要作用。由于天然存在三种稳定同位素（24Mg，78.992%；25Mg，10.003%；26Mg，11.005%），镁稳定同位素分馏可为这些循环提供见解。在此，我们首次详细阐述了高等植物小麦（Triticum aestivum L.）在其生长周期中的镁稳定同位素分布情况。小麦植株在养分供应受限的水培条件下生长，一部分任其成熟衰老，另一部分在成熟时去顶以收集渗出物。对叶绿素、种子、地上部分、根、叶、渗出物以及受限营养液随时间的镁同位素组成测量表明，植株似乎与可利用的养分建立了同位素平衡，并且随着植株成熟，植株（特别是种子和渗出物）以质量依赖关系在镁的重同位素中富集。植物对重镁同位素的偏好表明，由于收获导致重镁同位素的周期性去除，农业土壤和天然土壤中生物可利用镁可能存在差异。
