The Different Roles of Mineralogy in Soil Organic Carbon Accumulation in Northern and Southern China

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