Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms

Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms

2024 | Zibo Xu, Daniel C.W. Tsang
Soil is the largest terrestrial carbon reservoir, playing a central role in climate change and environmental health. Minerals contribute to over 60% of soil carbon storage, but the mechanisms by which mineral-organic carbon interactions influence carbon stability and transformation remain poorly understood. This review critically examines the primary interactions between organic carbon and soil minerals, including sorption, redox reactions, co-precipitation, dissolution, polymerization, and catalytic reactions. These interactions significantly affect organic carbon stability through processes such as mineral-organic carbon association formation, oxidative transformation, catalytic polymerization, and mineral transformation. Evidence from real eco-environmental interactions demonstrates the importance of these mechanisms in carbon turnover and stability. Current research gaps and priorities are highlighted, emphasizing the need for a deeper understanding of mineral-organic carbon interactions to improve soil carbon storage capacity. Mineral-organic carbon interactions are crucial for soil carbon stability. Sorption of organic carbon on minerals is vital, with different minerals having varying sorption capacities based on surface properties. Variably charged minerals can form non-charge minerals under specific conditions, while permanently charged minerals have a negative surface charge. These interactions influence organic carbon stability through electrostatic and ligand exchange mechanisms. Redox reactions between organic carbon and redox-active minerals are essential, with organic carbon acting as an electron donor, leading to mineral reduction and transformation. ROS (reactive oxygen species) generated through redox reactions or microbial activity can oxidize organic carbon, affecting its stability. Microbial-induced electron transfer between organic carbon and minerals is also significant, with microorganisms facilitating redox transformations that influence organic carbon degradation and mineral transformation. Mineral dissolution caused by organic carbon chelation or reduction is essential for organic carbon fate and mineral transformation. Co-precipitation of mineral ions and organic carbon forms stable complexes, influencing carbon and mineral element cycling. Polymerization of organic carbon with minerals increases its size and complexity, enhancing its stability against degradation. Catalytic transformation of organic carbon by minerals enhances reaction rates without altering the overall Gibbs energy change, through mechanisms such as increased oxidant concentration, orientation restriction, and electron transfer. These interactions significantly affect organic carbon stability, with mineral transformation altering binding affinity and stability. The stability of organic carbon is influenced by mineral properties, such as surface area, functionality, crystallinity, redox state, and solubility. Mineral transformations, such as crystallization or redox-related changes, can either stabilize or destabilize organic carbon, depending on the mineral properties and interactions. Overall, the complex interactions between minerals and organic carbon play a critical role in determining soil carbon stability and its long-term storage capacity.Soil is the largest terrestrial carbon reservoir, playing a central role in climate change and environmental health. Minerals contribute to over 60% of soil carbon storage, but the mechanisms by which mineral-organic carbon interactions influence carbon stability and transformation remain poorly understood. This review critically examines the primary interactions between organic carbon and soil minerals, including sorption, redox reactions, co-precipitation, dissolution, polymerization, and catalytic reactions. These interactions significantly affect organic carbon stability through processes such as mineral-organic carbon association formation, oxidative transformation, catalytic polymerization, and mineral transformation. Evidence from real eco-environmental interactions demonstrates the importance of these mechanisms in carbon turnover and stability. Current research gaps and priorities are highlighted, emphasizing the need for a deeper understanding of mineral-organic carbon interactions to improve soil carbon storage capacity. Mineral-organic carbon interactions are crucial for soil carbon stability. Sorption of organic carbon on minerals is vital, with different minerals having varying sorption capacities based on surface properties. Variably charged minerals can form non-charge minerals under specific conditions, while permanently charged minerals have a negative surface charge. These interactions influence organic carbon stability through electrostatic and ligand exchange mechanisms. Redox reactions between organic carbon and redox-active minerals are essential, with organic carbon acting as an electron donor, leading to mineral reduction and transformation. ROS (reactive oxygen species) generated through redox reactions or microbial activity can oxidize organic carbon, affecting its stability. Microbial-induced electron transfer between organic carbon and minerals is also significant, with microorganisms facilitating redox transformations that influence organic carbon degradation and mineral transformation. Mineral dissolution caused by organic carbon chelation or reduction is essential for organic carbon fate and mineral transformation. Co-precipitation of mineral ions and organic carbon forms stable complexes, influencing carbon and mineral element cycling. Polymerization of organic carbon with minerals increases its size and complexity, enhancing its stability against degradation. Catalytic transformation of organic carbon by minerals enhances reaction rates without altering the overall Gibbs energy change, through mechanisms such as increased oxidant concentration, orientation restriction, and electron transfer. These interactions significantly affect organic carbon stability, with mineral transformation altering binding affinity and stability. The stability of organic carbon is influenced by mineral properties, such as surface area, functionality, crystallinity, redox state, and solubility. Mineral transformations, such as crystallization or redox-related changes, can either stabilize or destabilize organic carbon, depending on the mineral properties and interactions. Overall, the complex interactions between minerals and organic carbon play a critical role in determining soil carbon stability and its long-term storage capacity.
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