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 depicting its intricate distribution. This study employed a two-stage approach to analyze soil structure: 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%). MAOC is more stable than POC within soil aggregate structures. The depletion of SOC resulted in consistent trends in pore volume distribution across all soil samples but led to variations in pore shape distribution between different soils, which, in turn, affect the function of soil aggregates. Experimental methods confirmed distinct cementation mechanisms for the two soil types: SOC plays a more crucial role in aggregate formation in Cambisol samples, while minerals have a greater influence on Ultisol aggregates. This study aims to move beyond the traditional "black box" view of soil by visualizing the complex interactions between soil organic carbon (SOC) and soil structure. This approach could provide valuable insights into the mechanisms behind soil aggregate formation.

Keywords: SOC, soil aggregates, SR- μCT, MAOC, POC, soil porosity