Newly-formed minerals in rhizosphere soils and its relevance in accelerated soil formation and to nutrient cycling

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Our recent work has advanced the understanding of the biologically-mediated mineral breakdown and nutrient cycling in rhizosphere soils (RS) and other terrestrial microenvironments (e.g., lichen/rock interface). The proposal will provide new information such as magnesium storage in hydroxy-interlayered clay minerals (HIM) - a possible new concept to evaluate the sustainability of non-fertilized soils through manipulation of clay mineral formation. The main experiments include growth chamber experiments to understand the formation of HIM from primary minerals in RS of common agricultural crops (e.g., barley, alfalfa) and forest species (e.g., hybrid spruce, sub-alpine fir). Illite, chlorite, mica and feldspars will be mixed with acid-washed Ottawa sand to create the experimental growth medium for each plant. Soil solution will be collected from the RS using microsuction cups and clay samples will be collected at the end of the growing period. Rhizosphere soils and lichen/rock interface materials will be collected in several field sites. Laboratory and field samples will be analyzed for clay mineral composition using x-ray diffraction, scanning electron microscopy and infrared spectroscopy. Other analytical methods include synchrotron radiation (e.g., x-ray absorption spectroscopy) to determine the oxidation state of major elements (e.g., Fe in chlorite and mica), nuclear magnetic resonance and inductively-coupled plasma atomic emission spectrometers, and capillary electrophoresis for chemical characterization of soils, rocks, plants and water samples. Identity of the organisms in RS and lichen/rock interface samples will be determined by 16S rDNA technique while organic acids and soil solution composition will be estimated using capillary electrophoresis. We hope to emphasize the critical role of organisms in biogeochemical processes and therefore the need to investigate the mosaic of microenvironments in soil systems, as well as raise awareness that properties measured from composite and bulk samples seldom represent the "functional" soil environments.