The sequestration of soil organic carbon (SOC) through mineral protection is an important approach to mitigating climate change. However, the effect of mineral composition on SOC stability is unclear at regional scales. In this study, we investigated the relationship between mineralogy and SOC in Alfisol and Mollisol from southern and northern regions of China. We analyzed soil at two layers for its SOC fractions, mineralogical characteristics and functional groups. It was found that the majority of SOC was stored as mineral-associated organic C (MAOC), which had higher δ¹³C values and narrower C/N ratios compared to particulate organic C. In Mollisol, the proportion of MAOC and the abundance of aromatic C were higher than that in Alfisol, while polysaccharide C was lower. Compared to Alfisol, Mollisol was dominated by illite, and had significantly (p < 0.05) lower iron (Fe) and aluminum (Al) sesquioxides contents. The SOC content was positively correlated with illite in Mollisol, and with Fe and Al sesquioxides in Alfisol. The random forest model identified sesquioxides as the most important determinant of SOC accumulation (36%), followed by SOC fractions (18%) and functional groups (18%). In summary, our study suggests that SOC protection through mineralogy depends more on the composition of the host minerals, and not just on the clay content, and aromatic C is also important in the stabilization of SOC.

Wheat straw is a plant-derived substrate rich in cellulose, hemicellulose, and lignin and represents a major carbon input to agricultural soils. Mineral-associated organic carbon (MAOC) is the most stable soil carbon pool, yet how mineral structure regulates the stability of straw-derived MAOC through microbial processing remains unclear. Here, straw-derived MAOC was formed in artificial soils containing five clay minerals (halloysite, kaolinite, illite, vermiculite, and montmorillonite) during a two-year incubation, followed by a 45-day incubation with a standardized microbial community to quantify CO₂ emission and net carbon balance. Mineral type regulated MAOC mineralization (38.54–54.48 mg C g⁻¹ MAOC). Vermiculite produced the highest CO₂ emission but maintained a positive net carbon balance, whereas illite showed net carbon loss (−0.53 g kg⁻¹). Kaolinite, halloysite, and montmorillonite exhibited lower mineralization and retained net carbon. The 2:1 clay minerals enhanced interlayer interactions and favored accumulation of C=O and aromatic compounds, reflecting stronger microbial transformation and residue retention. In contrast, 1:1 minerals stabilized carbon via edge hydroxyl bonding, which restricted substrate accessibility and slowed decomposition. Cumulative mineralization decreased with initial MAOC carbon but increased with dissolved organic carbon and bacterial abundance. Net carbon retention increased with N-acetylglucosaminidase activity and fungal abundance, indicating joint microbial control via nutrient acquisition and fungal processing. Two contrasting stabilization regimes were observed: high turnover driven by vermiculite and halloysite, and strong protection dominated by montmorillonite and kaolinite. These differences indicate that MAOC stability is jointly constrained by mineral-regulated accessibility and microbial transformation processes.

China has approximately 3.43 million hectares of tea plantations, which offer significant potential for carbon sequestration and the reduction of CO₂ emissions. However, the mechanisms underlying the stability and mineralization of soil organic carbon (SOC) in different tea plantations remain unclear. This study aimed to comprehensively evaluate the effects of chemical, physical, and microbial factors on SOC mineralization in tea plantations with different methods of forest conversion to tea plantations and different ages of tea plants. Our findings indicate that forest conversion to tea plantation methods and tea planting age significantly influence SOC mineralization. Specifically, the SOC mineralization in tea plantations reclaimed by clear-cutting and burning (FMT4) was lower than in those reclaimed by partial cutting (MT3, MT30, and MT150). This variation is attributed to differences in the chemical structure of SOC, which showed higher proportions of aromatic C (33.4%) and carbonyl/carboxyl C (7.8%), alongside lower proportions of O-alkyl C, in the FMT4 tea plantation compared to the others. Additionally, SOC mineralization was significantly higher in the MT150 tea plantation (15.23 g C kg⁻¹ SOC) than in the MT3 (10.11 g C kg⁻¹ SOC), MT30 (10.38 g C kg⁻¹ SOC), and MT200 plantations (9.13 g C kg⁻¹ SOC). Notably, although the MT200 tea plantation had a higher proportion of O-alkyl C (42.4%) than the MT3 and MT30 plantations (36.4%), and was similar to the MT150 plantation (43.1%), its SOC mineralization remained lower due to the higher clay content (278 g kg⁻¹). Correlation analysis and random forest analysis further revealed that physical properties, particularly clay content, are the most significant factors regulating SOC mineralization, followed by the chemical structure, such as O-alkyl C and aromatic C, as well as other physicochemical properties like the carbon-to-nitrogen (C/N) ratio, and microbial properties like Gram-positive bacteria. In conclusion, our study highlights the complex interplay of soil physical properties and SOM chemical structure and microbial properties in regulating SOC mineralization, providing valuable insights for improving carbon management in tea plantations.