Biologically-Mediated Weathering of minerals from Nanometre Scale to Environmental Systems.

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In nature, a complex system of physical, chemical and biological processes weather the Earth's surface and transform rock into soil. Because global erosion loss is now much faster (100 times or more) than soil formation, largely as a result of unsustainable cultivation practices, soil has become a finite resource. Despite the importance of soil for sustenance of our planet and it 6 billion human inhabitants, our knowledge of weathering is limited. This is because various scientific approaches are not sufficiently integrated to tackle the many, complex interactions that occur. Therefore a multi-disciplinary approach is needed to study soil formation rates and processes. Soil fungi appear to use plant energy to mine nutrients from rock-but the mechanisms involved are uncertain. We want to know if biological weathering is driven by the flow of sugar produced by plant photosynthesis in return for nutrient elements (such as phosphorous, potassium) from the mineral particles. Nearly a third of the total chemical energy (sugar) produced by forest trees passes directly to symbiotic (mutually beneficial) root fungi. These fungi completely cover the tree roots and form extensive networks of living threads through soil. Virtually all nutrients taken up by the trees are absorbed through these fungi. This research programme will identify how fungal cells, and their secretions, interact with mineral surfaces and affect the rates of nutrient transfer from minerals to the organism. Making biological processes central to molecular-level understanding of how minerals dissolve is counter to existing theories. Investigating these fundamental molecular mechanisms in living systems allows us to create new concepts and mathematical models that can describe biological weathering and be used in computer simulations of soil weathering dynamics. We propose to study these biochemical interactions at three levels of observation: 1.At the molecular scale to understand interactions between living cells and minerals and to quantify the chemistry that breaks down the mineral structure, 2.At the soil grain scale to quantify the activity and spatial distribution of the fungi, roots and other organisms (e.g. bacteria) and their effects on the rates at which minerals are dissolved to release nutrients, and 3.At soil profile scale to test models for the spatial distribution of active fungi and carbon energy and their seasonal variability and impact on mineral dissolution rates. We will combine the expertise from many scientific fields. Biologists will work with the fungi and plant cultures in the presence and absence of minerals that are sources of nutrients, and measure carbon energy fluxes in the fungal networks. Surface chemists will use X-Ray and Infrared beams that interact with the cell and mineral surface, and are then measured using sophisticated sensors to provide information on the chemical bonds that can form. Physicists will measure the minuscule forces that operate between fungi cells and minerals surfaces, but determine if fungi actually adhere and form chemical bonds. Materials scientists will use highly specialised visualisation methods to observe the shape and composition of dissolving minerals at almost atomic scale. Geochemists will study how the minerals change over time and how much mineral is dissolved. The data and understanding that is obtained, by working from almost molecular to soil profile scale, will be used by numerical modellers to simulate the complex interactions between higher plants, fungi, minerals, soil organic matter and infiltrating water. A final step is to simulate soil profile weathering under a range of scenarios for changes in climatic conditions and soil management. The anticipated achievement is a much stronger fundamental understanding of soil formation, particularly the role of biological weathering, so that we can improve our management strategies for this important natural resource.