Deng, Zizheng; Chen, Chong; Wang, Xiang; Shang, Jianying; Zhou, Hu
Abstract
Soil organic matter (OM) plays a vital role in regulating specific surface area (SSA) and nanopore structure. However, the respective contributions of particulate organic matter (POM) and mineral-associated organic matter (MAOM) to SSA and nanopore characteristics remain poorly understood. In this study, five representative soils with varying organic carbon (OC) content (1.74-3.73%) and different mineralogies collected from grassland (G), paddy field (P), forestland (F), cropland (C), and vegetable field (V) were physically fractionated into coarse (53-2000 mu m) and fine (< 53 mu m) particles. The SSA measured by N-2 and H2O adsorption (SSA(N2) and SSA(H2O)), micropore and mesopore volumes (V-micro and V-meso), as well as N-2 hysteresis characteristics were measured before and after OM removal. Results showed that OM exerted a stronger masking effect on SSA(N2) in fine fractions, especially in soils rich in 2:1 clay minerals. In contrast, OM enhanced SSA(H2O) in coarse fractions and kaolinite-dominated fine fractions (e.g., P), whereas its effect on SSA(H2O) in fine fractions rich in 2:1 clays remained ambiguous. OM removal significantly increased both V-micro and V-meso in most soils, with a more pronounced effect in fine fractions, particularly those with initially abundant nanopores. The extent of nanopore reduction was positively correlated with OC content, indicating that OM-induced pore blocking depends on both pore abundance and OM load. Furthermore, OM increased hysteresis effects, especially in mesopores, by narrowing pore throats and decreasing pore connectivity. These findings reveal how OM, influenced by particle size, mineralogy, and OC content, regulates soil microstructure, providing a basis for enhancing carbon stabilization, water retention, and ecological functioning.
Regulation of mineral surface area and nanopore structures by particulate and mineral-associated organic matter.pdf