Spatiotemporal characterisation of the soil redox status within the capillary fringe (CF) is a challenging task. Air-filled porosities (ε), oxygen concentration (O₂) and soil redox potential (E_H) are interrelated soil variables within active biogeochemical domains such as the CF. We investigated the impact of water table (WT) rise and drainage in an undisturbed topsoil and subsoil sample taken from a Calcaric Gleysol for a period of 46 days. We merged 1D (E_H and matric potential) and 2D (O₂) systems to monitor at high spatiotemporal resolution redox dynamics within self-constructed redoxtron housings and complemented the data set by a 3D pore network characterization using X-ray microtomography (X-ray μCT). Depletion of O₂ was faster in the organic matter- and clay-rich aggregated topsoil and the CF extended >10 cm above the artificial WT. The homogeneous and less-aggregated subsoil extended only 4 cm above the WT as indicated by ε–O₂–E_H data during saturation. After drainage, 2D O₂ imaging revealed a fast aeration towards the lower depths of the topsoil, which agrees with the connected ε derived by X-ray μCT (ε_{CT_conn}) of 14.9% of the total porosity. However, small-scaled anoxic domains with O₂ saturation <5% were apparent even after lowering the WT (down to 0.25 cm² in size) for 23 days. These domains remained a nucleus for reducing soil conditions (E_H < −100 mV), which made it challenging to characterise the soil redox status in the CF. In contrast, the subsoil aeration reached O₂ saturation after 8 days for the complete soil volume. Values of ε_{CT_conn} around zero in the subsoil highlighted that soil aeration was independent of this parameter suggesting that other variables such as microbial activity must be considered when predicting the soil redox status from ε alone. The use of redoxtrons in combination with localised redox-measurements and image based pore space analysis resulted in a better 2D/3D characterisation of the pore system and related O₂ transport properties. This allowed us to analyse the distribution and activity of microbiological niches highly associated with the spatiotemporal variable redox dynamics in soil environments.

中文翻译：

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Redoxtrons——一种研究毛细管边缘内氧化还原过程的实验系统

毛细管边缘 (CF) 内土壤氧化还原状态的时空表征是一项具有挑战性的任务。充气孔隙率 (ε)、氧气浓度 (O ₂ ) 和土壤氧化还原电位 (E _H ) 是活性生物地球化学领域（例如 CF）内相互关联的土壤变量。我们调查了地下水位 (WT) 上升和排水对从 Calcaric Gleysol 采集的未受干扰的表土和底土样品的影响，为期 46 天。我们合并了 1D（E _H和基质势）和 2D (O ₂ ) 系统以监测自建氧化还原外壳内的高时空分辨率氧化还原动力学，并通过使用 X 射线显微断层扫描（X-射线μCT）。O耗尽₂在富含有机质和粘土的聚合表土中更快，并且 CF 在人工 WT 上方延伸 > 10 厘米。如饱和期间的 ε–O ₂ –E _H数据所示，均质且聚集较少的底土仅在 WT 以上延伸 4 厘米。排水后，2D O ₂成像显示向表层土的较低深度快速通气，这与 X 射线 μCT (ε _{CT_conn} ) 得出的连接 ε 占总孔隙率的 14.9% 一致。然而，即使在将 WT（大小降至 0.25 cm ^{2 ）降低 23 天后，O} ₂饱和度 <5%的小规模缺氧区域也很明显。这些领域仍然是减少土壤条件的核心（E _H < −100 mV)，这使得表征 CF 中的土壤氧化还原状态具有挑战性。相比之下，对于完整的土壤体积，底土通气在 8 天后达到 O _{2饱和度。}底土中ε _{CT_conn的值在零附近突出表明土壤通气与该参数无关，这表明在仅从 ε 预测土壤氧化还原状态时必须考虑其他变量，例如微生物活动。}将氧化还原仪与局部氧化还原测量和基于图像的孔隙空间分析相结合，可以更好地对孔隙系统和相关 O _{2进行 2D/3D 表征}传输属性。这使我们能够分析与土壤环境中时空变量氧化还原动力学高度相关的微生物生态位的分布和活动。