An isotopic study of abiotic nitrite oxidation by ligand-bound manganese (III)
An isotopic study of abiotic nitrite oxidation by ligand-bound manganese (III)
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DOI：
10.1016/j.gca.2020.11.004
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发表时间：
2021-01-15
影响因子：
5
通讯作者：
Wankel, Scott D.
中科院分区：
文献类型：
--
作者：
Karolewski, Jennifer S.;Sutherland, Kevin M.;Wankel, Scott D.
氮的氧化还原转化在决定其形态和生物有效性方面起着关键作用，从而决定了许多生态系统生产力的大小和范围。一系列重要的氮转化往往同时发生在其他氧化还原活性元素，包括硫，铁，锰（Mn），特别是沿着急剧的氧化还原梯度内的水生沉积物的区域。这种“氧化还原真实的状态”的接近产生了多元素相互作用和耦合循环的有利条件。虽然以前的工作已经报道了缺氧硝化与沉积物中锰（Mn）氧化物的存在有关，但Mn和N的循环之间的明确联系仍然难以捉摸。可溶性锰（III），这是通过配体络合稳定，最近已被证明是代表在许多环境中的主要溶解锰物种。在这里，我们研究了配体稳定的Mn（III）与亚硝酸盐的反应性，使用天然丰度稳定的氮和氧同位素，在一系列条件下探索反应动力学。在充氧和氮气吹扫条件下，Mn（III）-焦磷酸盐将亚硝酸盐氧化为硝酸盐进行非生物氧化。该反应的动力学和同位素系统学在pH值范围内（5-8）进行了测量，反应速率随pH值增加而降低。在所有处理下，观察到N的逆动力学同位素效应为-19.9 +/-0.7%，与先前记录的亚硝酸盐氧化生物分馏非常相似。使用O-18标记的水进行的实验证实了额外氧原子的来源是水。这些研究结果表明，亚硝酸盐氧化环境中托管丰富的配体结合锰（III），包括孔隙沃茨，河口，沿海沃茨，可能会促进部分非生物反应与锰，即使在功能缺氧条件下。(C)2020爱思唯尔有限公司版权所有。
Redox transformations of nitrogen (N) play a critical role in determining its speciation and biological availability, thus defining the magnitude and extent of productivity in many ecosystems. A range of important nitrogen transformations often co-occur in regions hosting other redox-active elements, including sulfur, iron, and manganese (Mn), especially along sharp redox gradients within aquatic sediments. This proximity in "redox real estate" produces conditions under which multielement interactions and coupled cycling are thermodynamically favored. While previous work has reported anoxic nitrification linked to the presence of manganese (Mn) oxides in sediments, a clear connection between the cycling of Mn and N has remained elusive. Soluble Mn(III), which is stabilized via ligand-complexation, has recently been shown to represent the dominant dissolved Mn species in many environments. Here, we examined the reactivity of ligand-stabilized Mn(III) with nitrite, using natural abundance stable nitrogen and oxygen isotopes to explore reaction dynamics under a range of conditions. Oxidation of nitrite to nitrate by Mn(III)-pyrophosphate proceeded abiotically under both oxygen replete and nitrogen-purged conditions. Kinetics and isotope systematics of this reaction were measured over a range of pH (5-8), with reaction rates decreasing with increasing pH. Under all treatments, an inverse kinetic isotope effect of -19.9 +/- 0.7% was observed for N, remarkably similar to previously documented fractionation by nitrite-oxidizing organisms. Experiments using O-18-labeled water confirmed that the source of the additional oxygen atom was from water. These findings suggest that nitrite oxidation in environments hosting abundant ligand-bound Mn(III), including porewaters, estuaries, and coastal waters, may be facilitated in part by abiotic reactions with Mn, even under functionally anoxic conditions. (C) 2020 Elsevier Ltd. All rights reserved.