Mechanisms and influencing factors of soil organic carbon sequestration by minerals

Soils, which play an active role in the global carbon cycle, are the largest store of carbon in terrestrial ecosystems. Considering the increasing seriousness of the greenhouse effect, it is of utmost importance to enhance the stability of organic carbon in soil. Previous studies have verified that mineral sorption is one of the most significant organic carbon stabilization mechanisms. The capacity and stability of the organic carbon adsorbed by minerals are affected by multiple factors. Soil mineral type, crystallinity, and mineral particles sizes affect the mineral adsorption capacity and mechanism. Amorphous phase minerals such as allophane and imogolite have a strong adsorption capacity for organic carbon. It is widely accepted that plant-derived carbon is preferentially adsorbed by coarse minerals and microbial-derived carbon is strongly adsorbed by fine minerals. This is because microbial-derived mineral-associated organic carbon formed by microbial pathways is enriched in areas of microbial “hot spots”, namely mineral surface pores. Microorganism degradation of soil organic carbon has a dual effect on the formation of mineral-bound organic carbon. On one hand, microorganisms and minerals compete for reactive organic carbon; thereafter, one part of the carbon is mineralized into CO₂, and the other part is converted into microbial biomass carbon, which is recycled by microorganisms or adsorbed by minerals. On the other hand, microorganisms degrade resistant organic carbon, and as a result, partially processed organic carbon is more easily adsorbed by minerals. The assimilation of plant-derived carbon into microbial biomass carbon is an important precursor for soil organic carbon stabilization. Microbial degradation of soil organic carbon reduces the molecular size of biomolecules and adds oxygen-containing functional groups to soil organic carbon, both of which are essential for mineral adsorption of organic carbon in the soil. Besides the aforementioned factors, soil physical and chemical properties and land use affect the mineral adsorption capacity. It is indisputable that the mineral adsorption mechanism plays an important role in soil organic carbon storage. It is beneficial to increase organic carbon storage in the soil to study the mechanism and factors of mineral adsorption of soil organic carbon. We have summarized previous studies related to soil organic carbon and soil minerals. The objectives of this study were to explore the correlation law of mineral immobilization of organic carbon in the soil and to provide a theoretical basis for increasing soil organic carbon storage and for mitigating the effects of climate warming on soil organic carbon storage.