Ectomycorrhizal Fungi and Mineral Interactions in the Rhizosphere of Scots and Red Pine Seedlings

Ectomycorrhizal fungi and associated bacteria play a key role in plant-driven mineral weathering and uptake of mineral-derived nutrients in the rhizosphere. The goal of this study was to investigate the physical and chemical characteristics of bacteria-fungi-mineral interactions in biofilms of Scots and red pine rhizospheres. In three experiments, seedlings were grown in columns containing silica sand amended with biotite and calcium-feldspar, and inoculated with pure cultures of ectomycorrhizal fungi or a soil slurry. Uninoculated seedlings and unplanted abiotic columns served as controls. After nine months, the columns were destructively sampled and the minerals were analyzed using scanning electron and atomic force microscopy. Element release rates were determined from cation concentrations of input and output waters, soil exchange sites, and plant biomass, then normalized to geometric surface area of minerals in each column. The results revealed that various ectomycorrhizal fungal species stimulate silicate dissolution, and biofilm formation occurred at low levels, but direct surface attachment and etching by fungal hyphae was a minor contributor to the overall cation release from the minerals in comparison to other environmental conditions such as water applications (rain events), which varied among the experiments. This research highlights the importance of experimental design details for future exploration of these relationships.