PLANT-DRIVEN ECTOMYCORRHIZAL WEATHERING OF SILICATE MINERALS

Biota is one of the main soil forming factors, and it has been well documented that plants and associated microbes can influence the rate and trajectory of weathering processes during transforming rocks to soil. Ectomycorrhizal fungi (a symbiont) play a key role in mineral-sourced nutrient acquisition in the root zone. It has been postulated that during nutrient-limited conditions ectomycorrhizae provide an advantage in foraging and improve plant health. However, quantifying the effects of biota on weathering is challenging because biotic and abiotic processes and hydrological transport are interconnected in the Critical Zone environment. In addition, ongoing environmental change affects vegetation distribution and productivity and is most likely influencing plants interactions with rocks and biogeochemical cycles of mineral-sourced elements. In this presentation, I summarize the results of three mesocosm experiments, which aimed to investigate the physical and chemical characteristics of the interactions among minerals, ectomycorrhizal fungi and associated bacteria in pine rhizospheres. In the laboratory, pine seedlings were grown in columns containing silica sand amended with biotite and calcium-feldspar (sole sources of potassium and calcium) and inoculated with either pure cultures of ectomycorrhizal fungi or a soil slurry. Seedlings without fungi and/or bacteria and unplanted abiotic columns served as controls. After 9 months, the columns were destructively sampled and the minerals were analyzed using microscopy and spectroscopy techniques. Drainage water was also collected, and element release rates were determined from cation concentrations of input and output waters, soil exchange sites, and plant biomass then normalized to the geometric surface area of minerals in each column. The results show that various ectomycorrhizal fungal species stimulate silicate dissolution, cause elemental depletion of mineral surfaces, form etching patterns and transform minerals to secondary phases. However, the results suggest that environmental factors, such as water availability (varied among the experiments) impacts the weathering ability of the plants and their symbionts. Thus, it highlights the importance of future explorations of these interactions under the changing environment.