The abundance and oxidation states (II, III and IV) of manganese (Mn) in a weathering profile encompassing both the soil layers (A and B horizons) and the underlaid saprolite (C horizons) determine the availability of Mn as a plant nutrient and regulate its role in cycles of other elements in Earth’s critical zone. However, it remains unclear how the abundance and oxidation states vary with depth under different climates, and how the soil forming processes and soil properties control the variations. We examined four forest granite weathering profiles developed under climates ranging from temperate to tropical climate. Regardless of climate types, all four profiles showed similar vertical variation patterns of Mn concentration and oxidation states. The major features of the patterns can be understood from the perspective of soil forming processes and soil properties. Climate affected the Mn oxidation states in the fine fraction (< 2 mm; i.e., the soil fraction) of the poorly weathered saprolite by controlling the weathering degree of Mn-bearing primary minerals. The weathering released Mn(II) and Mn(III) in the primary minerals to the circumneutral environment where it was subsequently oxidized by O2. In contrast, climate affected the Mn oxidation states in the soil layers poor in parent materials largely by controlling soil redox conditions and pH because most of the Mn in soils was reactive. As the climate became warmer/wetter, the weathering intensified and soils became more reducing and acidic, resulting in more reduced Mn in the soil layers but more oxidized Mn in the fine fraction of saprolite. Moreover, relative to Mn(II) and Mn(IV), Mn(III) preferentially accumulated in the subsoil (B horizons), likely as Mn(III) oxyhydroxides in the colder and drier climates, and as a substitute ion in well-crystallized Fe(III) oxides in the warmer and wetter climates. These findings improve our understanding of Mn availability and cycling and its role in biogeochemical cycles of other elements in Earth’s critical zone.

中文翻译：

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锰的氧化态和在对比气候的森林风化剖面中的可用性


锰 （Mn） 在包括土壤层（A 和 B 层）和下层腐泥岩（C 层）的风化剖面中的丰度和氧化态（II、III 和 IV）决定了锰作为植物养分的可用性，并调节其在地球临界区其他元素循环中的作用。然而，目前尚不清楚在不同气候下丰度和氧化态如何随深度变化，以及土壤形成过程和土壤特性如何控制这些变化。我们研究了在从温带到热带气候的气候下形成的四种森林花岗岩风化剖面。无论气候类型如何，所有 4 个剖面都显示出相似的 Mn 浓度和氧化态的垂直变化模式。可以从土壤形成过程和土壤特性的角度来理解这些模式的主要特征。气候通过控制含 Mn 原生矿物的风化程度，影响了风化不良腐泥岩细小部分（< 2 mm;即土壤部分）的 Mn 氧化态。风化作用将原生矿物中的 Mn（II） 和 Mn（III） 释放到中性环境中，随后被 O2 氧化。相比之下，气候主要通过控制土壤氧化还原条件和 pH 值来影响母质贫乏土壤层中的 Mn 氧化态，因为土壤中的大部分 Mn 是反应性的。随着气候变得更温暖/更潮湿，风化作用加剧，土壤变得更加还原和酸性，导致土壤层中锰的还原量增加，而腐泥石的细小部分中的氧化锰含量增加。 此外，相对于 Mn（II） 和 Mn（IV），Mn（III） 优先积累在底土（B 层）中，在较冷和干燥的气候中可能以 Mn（III） 氧基氧化物的形式积累，在较温暖和潮湿的气候中以充分结晶的 Fe（III） 氧化物的形式作为替代离子。这些发现提高了我们对 Mn 可用性和循环及其在地球关键区其他元素的生物地球化学循环中的作用的理解。