FUNGAL-MINERAL INTERACTIONS - BIOTITE WEATHERING

The presence of ectomycorrhizal fungi in the rhizosphere (root zone) enhances mineral weathering that has been well documented in soil environments and laboratory experiments. In addition, fungi influence the accumulation and stabilization of carbon in the root zone. These processes significantly influence soil formation on short timescales, while abiotic weathering dominates soil formation on longer terms. This presentation summarizes results from laboratory experiments and field mesh-bag studies that focused on understanding processes at the plant-microbe-mineral interface using biotite as the tested mineral. We investigated the role of the direct attachment of bacteria and fungi to mineral surfaces in weathering, secondary product formation, and carbon stabilization. These studies were based on the principle that plants provide the photosynthetic energy (carbon) that drives microorganisms and fungi to enhance mineral weathering that results in nutrient release for the immediate needs of the plants, fungi, and microorganisms. Simultaneously, secondary phases of minerals form that provide sinks for unneeded elements and surfaces for nutrient and soil organic carbon accumulation. The studies utilized various bulk and surface-specific techniques to estimate chemical changes and visualized mineral transformations at all scales. We estimated lithogenic elements weathered using amounts of cations in drainage and soil waters, plant biomass, and soil exchangeable sites determined by various spectroscopic techniques. We characterized mineral surface changes and carbon stabilization using scanning and transmission electron microscopy and atomic force microscopy methods. While the applied techniques were unable to separate and quantify abiotic and biotic weathering, they provided supporting evidence of fungal enhancement of mineral weathering, soil formation, and carbon stabilization.