Investigating the influence of soil organic carbon on pore structure within aggregates a comparative study of Ultisols and Cambisols in China

Soil pore structure, dictated by factors such as porosity, size distribution, and geometry, is crucial for various soil processes and is significantly influenced by soil organic carbon (SOC). As the primary architect of pore geometry within soil aggregates, SOC plays a vital role in determining soil functionality and ecosystem services, yet traditional in-situ analysis methods have fallen short in accurately depicting its intricate distribution. The study employed a two-fold 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 hydrogen peroxide treatment variably reduced organic carbon in soil aggregates, with Cambisol showing a higher removal efficiency (68-79%) compared to Ultisol (42-47%). The data highlighted the transformation of smaller pores and an increase in larger pore spaces following organic carbon removal, with Cambisol aggregates experiencing the most substantial alterations in pore structures. The impact of organic carbon on the shaping of pore structure within soil aggregates was profound and varied distinctly between the two studied soils—Ultisol and Cambisol. In Ultisol, the organic carbon, initially minimal, played a subtle role in pore structure formation, leading to limited changes post-removal, which suggested a structural resilience possibly due to its inherent mineralogy and physicochemical characteristics. In contrast, Cambisol, with higher initial organic carbon content, showed dramatic alterations in pore structure upon organic carbon removal. This indicated a more critical role of organic carbon in maintaining pore space configurations, with significant increases in larger pore spaces and a decrease in smaller, disconnected pores. These changes highlighted the organic carbon’s crucial function in not only sustaining pore integrity but also in facilitating the complex soil functions such as water retention and root penetration.