Interactions between organic matter and minerals for soil carbon sequestration

Abstract

The processes and mechanisms that govern soil organic carbon (SOC) sequestration are a central focus of environmental research because their critical influence in soil function and climate regulation. Soil mineral mediated retention and stabilisation of mineral associated organic matter (MAOM) represents the major pathway for the long-term carbon storage. However, the investigation of mineral-organic interactions is constrained by the inherent complexity of both organic fractions such as dissolved organic matter (DOM) and mineral phases (i.e., phyllosilicates and metal oxides), the influence of external conditions related to land use, and the limitations in available analytical techniques. This thesis investigates the heterogeneity and chemical convergence of DOM derived from common Australian plant residues using multiple analytical techniques coupled with multivariate analysis. This thesis synthesises prototype MAOM by systemically interacting DOM with a range of mineral phases to reveal the sequential and selectivity of organic compounds on mineral surfaces with contrasting properties. This thesis also evaluates the utility of optical photothermal infrared (OPTIR) spectroscopy for revealing key functional group information at mineral-organic interfaces in both synthetic and natural MAOM at submicron spatial resolution. This thesis examines the effect of land use conversion from native vegetation to cropping on the concentration and molecular composition of OM associated with different mineral phases in a Ferrasol. Overall, this thesis establishes a mechanistic and analytical framework that links DOM composition, mineral surface chemistry, and land use conversation to the formation and persistence of MAOM, and it provides a robust foundation for improving long-term SOC storage to support soil function and climate regulation.