Minerals constitute a primary ecosystem control on organic C decomposition in soils, and therefore on greenhouse gas fluxes to the atmosphere. Secondary minerals, in particular, Fe and Al (oxyhydr)oxides-collectively referred to as "oxides" hereafter-are prominent protectors of organic C against microbial decomposition through sorption and complexation reactions. However, the impacts of Mn oxides on organic C retention and lability in soils are poorly understood. Here we show that hydrous Mn oxide (HMO), a poorly crystalline δ-MnO2, has a greater maximum sorption capacity for dissolved organic matter (DOM) derived from a deciduous forest composite Oi, Oe, and Oa horizon leachate ("O horizon leachate" hereafter) than does goethite under acidic (pH 5) conditions. Nonetheless, goethite has a stronger sorption capacity for DOM at low initial C:(Mn or Fe) molar ratios compared to HMO, probably due to ligand exchange with carboxylate groups as revealed by attenuated total reflectance-Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy and scanning transmission X-ray microscopy-near-edge X-ray absorption fine structure spectroscopy coupled with Mn mass balance calculations reveal that DOM sorption onto HMO induces partial Mn reductive dissolution and Mn reduction of the residual HMO. X-ray photoelectron spectroscopy further shows increasing Mn(II) concentrations are correlated with increasing oxidized C (C=O) content (r = 0.78, P < 0.0006) on the DOM-HMO complexes. We posit that DOM is the more probable reductant of HMO, as Mn(II)-induced HMO dissolution does not alter the Mn speciation of the residual HMO at pH 5. At a lower C loading (2 × 102 μg C m-2), DOM desorption-assessed by 0.1 M NaH2PO4 extraction-is lower for HMO than for goethite, whereas the extent of desorption is the same at a higher C loading (4 × 102 μg C m-2). No significant differences are observed in the impacts of HMO and goethite on the biodegradability of the DOM remaining in solution after DOM sorption reaches steady state. Overall, HMO shows a relatively strong capacity to sorb DOM and resist phosphate-induced desorption, but DOM-HMO complexes may be more vulnerable to reductive dissolution than DOM-goethite complexes.

中文翻译：

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含水锰氧化物对溶解有机物的保留和不稳定性的影响。

矿物是土壤中有机碳分解的主要生态系统控制，因此也是温室气体向大气通量的控制。次生矿物，特别是Fe和Al（羟基）氧化物（以下统称为“氧化物”）是有机C的重要保护剂，可防止微生物通过吸附和络合反应分解。但是，人们对锰氧化物对土壤中有机碳保留和不稳定性的影响知之甚少。在这里，我们显示出水合的氧化锰（HMO），一种较差的δ-MnO2，对落叶森林复合材料Oi，Oe和Oa地平线浸出液（“ O地平线浸出液”）产生的最大溶解有机物（DOM）的最大吸附能力。 ”，以下是针铁矿在酸性（pH 5）条件下的情况。尽管如此，与HMO相比，针铁矿在较低的C：（Mn或Fe）初始摩尔比下对DOM具有更强的吸附能力，这可能是由于衰减的全反射-傅里叶变换红外光谱显示，配体与羧酸根发生了交换。X射线光电子能谱和扫描透射X射线显微镜-近边缘X射线吸收精细结构光谱结合Mn质量平衡计算表明，DOM吸附到HMO上会引起部分Mn还原溶解和残留HMO的Mn还原。X射线光电子能谱进一步显示，在DOM-HMO配合物中，Mn（II）浓度的增加与氧化C（C = O）含量的增加相关（r = 0.78，P <0.0006）。我们认为DOM是HMO的更可能还原剂，因为Mn（II）诱导的HMO溶解不会改变pH 5下残留HMO的Mn形态。在较低的C负载（2×102μgC m-2）下，通过0.1 M NaH2PO4萃取进行DOM解吸HMO比针铁矿要低，而在较高的C负荷（4×102μgC m-2）下，解吸的程度是相同的。在DOM吸附达到稳态后，HMO和针铁矿对溶液中残留DOM的生物降解性的影响没有观察到显着差异。总体而言，HMO表现出较强的吸附DOM和抵抗磷酸盐诱导的脱附的能力，但DOM-HMO复合物可能比DOM-针铁矿复合物更易于还原溶解。而在较高的碳负荷下（4×102μgC m-2），解吸的程度是相同的。在DOM吸附达到稳态后，HMO和针铁矿对溶液中残留DOM的生物降解性的影响没有观察到显着差异。总体而言，HMO表现出较强的吸附DOM和抵抗磷酸盐诱导的脱附的能力，但DOM-HMO复合物可能比DOM-针铁矿复合物更易于还原溶解。而在较高的碳负荷下（4×102μgC m-2），解吸的程度是相同的。在DOM吸附达到稳态后，HMO和针铁矿对溶液中残留DOM的生物降解性的影响没有观察到显着差异。总体而言，HMO表现出较强的吸附DOM和抵抗磷酸盐诱导的脱附的能力，但DOM-HMO复合物可能比DOM-针铁矿复合物更易于还原溶解。