Release and transport of organic carbon (OC), a large portion of which is complexed with mineral colloids, can lead to long-term C sequestration. However, the role of mobile colloids in carbon cycling is not well understood. In this study, we conducted experiments using syringe columns to measure size-dependent colloid mobility and associated OC loadings under stepwise reductions of redox potential, representing existence of different electron acceptors. Colloids were extracted from both leachate and soil samples, designated as leachate colloids and soil colloids, respectively, and fractionated into different sizes: particulates (450–1000 nm), fine colloids (100–450 nm) and nano colloids (2–100 nm) using sequential centrifugation and ultrafiltration techniques. Increases in leachate solution pH and ionic strength (IS) with decreasing redox potential promoted colloid release, as indicated in the increase in turbidity values, due to increased electrostatic repulsion between colloids and soil matrix. The average OC loading by colloids, i.e., the amount of OC associated with per unit mass of colloids, in leachate colloids was up to four times that of soil colloids for the same size fraction. In addition, fine colloids had ∼2 times higher OC loading (∼0.4 mg C mg colloids) than particulates (∼0.2 mg C mg colloid) for leachate colloids. Moreover, measurements of C:N ratio and the natural abundance of stable δC and δN isotope signatures of soil colloids showed that the fine-colloid fraction experienced more significant fluctuations in these measurements as redox potential decreased than the other two fractions (i.e., particulates and nano colloids). The results of this study demonstrated that OC loading, composition and reactivity all varied with size and strongly influenced by redox conditions. This knowledge can help improve the understanding of how different phases of OC, e.g., dissolved vs. colloidal OC, may impact C sequestration and transport in soils.

中文翻译：

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氧化还原电位逐步降低后土壤胶体的尺寸依赖性迁移率和相关的有机碳负载能力


有机碳（OC）的释放和运输（其中很大一部分与矿物胶体络合）可导致长期碳封存。然而，移动胶体在碳循环中的作用尚不清楚。在这项研究中，我们使用注射器柱进行了实验，以测量氧化还原电位逐步降低时依赖于尺寸的胶体迁移率和相关的 OC 负载，代表不同电子受体的存在。从渗滤液和土壤样品中提取胶体，分别命名为渗滤液胶体和土壤胶体，并分为不同尺寸：颗粒物（450-1000 nm）、细小胶体（100-450 nm）和纳米胶体（2-100 nm） ）使用顺序离心和超滤技术。渗滤液 pH 值和离子强度 (IS) 的增加以及氧化还原电位的降低促进了胶体释放，如浊度值增加所示，这是由于胶体与土壤基质之间的静电排斥力增加所致。渗滤液胶体中胶体的平均 OC 负载量，即与每单位质量胶体相关的 OC 量，高达相同尺寸部分的土壤胶体的四倍。此外，细小胶体的 OC 负载（～0.4 mg C mg 胶体）比渗滤液胶体颗粒（～0.2 mg C mg 胶体）高～2 倍。此外，土壤胶体的 C:N 比以及稳定 δ13C 和 δ1N 同位素特征的自然丰度的测量表明，随着氧化还原电位比其他两个部分（即颗粒物和颗粒物）下降，细粒胶体部分在这些测量中经历了更显着的波动。纳米胶体）。 这项研究的结果表明，OC 负载量、组成和反应性均随尺寸的变化而变化，并受氧化还原条件的强烈影响。这些知识可以帮助加深对不同相的 OC（例如溶解态 OC 与胶体 OC）如何影响土壤中碳封存和迁移的理解。