Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions
Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions
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DOI：
10.1016/j.epsl.2016.09.025
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发表时间：
2016-11-15
影响因子：
5.3
通讯作者：
Canfield，Donald E.
中科院分区：
文献类型：
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作者：
Scholz，Florian;Loescher，Carolin R.;Canfield，Donald E.
铁是地球上生命的基本元素，限制了海洋大部分地区的初级生产。无氧大陆边缘沉积物是海洋生物可利用铁的重要来源，但从海床释放的铁很少到达富饶的海面。即使在含氧量最低的缺氧水中，铁的溶解度应该提高，大多数铁也会迅速重新沉淀。为了约束缺氧海洋区域的除铁机制(S)，我们探索了秘鲁近海最低含氧区的沉积物和水。在我们的采样过程中，水柱有两个明显的氧化还原边界，将氧与硝酸盐还原(即含氮)水分开，将氮与弱硫化物水分开。与陆架沉积物接触的硫化物水团含有升高的铁浓度>；300 nm。在硫化和氮化条件的交界处，铁浓度急剧下降到<；20 NM，与颗粒铁浓度的最大值一致。在铁梯度中，我们发现硝酸盐还原的关键功能标记基因(NARG)的表达增加。这种上调在一定程度上与已知的铁氧化细菌的活性有关。总而言之，我们的数据表明，铁的氧化和去除是由硝酸盐还原微生物诱导的，要么是通过厌氧铁氧化，要么是通过为非生物反应提供亚硝酸盐。鉴于铁在固氮、光合作用和呼吸作用中的重要作用，依赖于硝酸盐的铁氧化很可能是海洋生物氮、氧和碳生物地球化学循环之间的关键环节。
Iron is an essential element for life on Earth and limits primary production in large parts of the ocean. Oxygen-free continental margin sediments represent an important source of bioavailable iron to the ocean, yet little of the iron released from the seabed reaches the productive sea surface. Even in the anoxic water of oxygen minimum zones, where iron solubility should be enhanced, most of the iron is rapidly re-precipitated. To constrain the mechanism(s) of iron removal in anoxic ocean regions we explored the sediment and water in the oxygen minimum zone off Peru. During our sampling campaign the water column featured two distinct redox boundaries separating oxic from nitrate-reducing (i.e., nitrogenous) water and nitrogenous from weakly sulfidic water. The sulfidic water mass in contact with the shelf sediment contained elevated iron concentrations >300 nM. At the boundary between sulfidic and nitrogenous conditions, iron concentrations dropped sharply to <20 nM coincident with a maximum in particulate iron concentration. Within the iron gradient, we found an increased expression of the key functional marker gene for nitrate reduction (narG). Part of this upregulation was related to the activity of known iron-oxidizing bacteria. Collectively, our data suggest that iron oxidation and removal is induced by nitrate-reducing microbes, either enzymatically through anaerobic iron oxidation or by providing nitrite for an abiotic reaction. Given the important role that iron plays in nitrogen fixation, photosynthesis and respiration, nitrate-dependent iron oxidation likely represents a key-link between the marine biogeochemical cycles of nitrogen, oxygen and carbon.