Investigating the influence of soil organic carbon on pore structure within aggregates

Abstract

Soil pore structural properties, such as porosity, size distribution and geometry, are crucial for various soil processes and are significantly influenced by soil organic carbon (SOC). SOC plays a vital role in determining soil functionality and ecosystem services and is the primary driver of pore geometry within soil aggregates, yet traditional in-situ analysis methods have fallen short in accurately describing its intricate distribution. This study employed a two-stage approach to analyze soil structure at the pore scale: a hydrogen peroxide fogging system was used to selectively remove organic carbon from soil aggregates, followed by synchrotron radiation micro-computed tomography (SR-μCT) for in-depth three-dimensional imaging. The results revealed that the hydrogen peroxide treatment variably reduced organic carbon in soil aggregates, with Cambisol samples showing a higher removal efficiency (38.58–63.31%) compared to Ultisol samples (27.33–45.74%). Mineral-associated organic carbon (MAOC) was more stable than particle organic carbon (POC). SOC depletion led to consistent changes in pore volume across soil types, but the changes in pore shape distribution varied between Cambisols and Ultisols. In Cambisols, SOC removal was associated with more pronounced shifts in pore morphology, whereas Ultisols showed more heterogeneous responses, likely due to differing mineralogical properties. These findings suggest that SOC contributes differently to pore structure depending on soil type. This study aimed to move beyond the traditional “black box” view of soil by visualizing the complex interactions between soil organic carbon (SOC) and soil structure with a new method. This approach could provide valuable insights into the mechanisms behind soil aggregate formation.