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

在自然界中，一个复杂的物理、化学和生物过程系统使地球表面受冻，并将岩石转化为土壤。由于全球水土流失速度现在比土壤形成快得多(100倍或更多)，这主要是不可持续的耕作做法造成的，土壤已经成为一种有限的资源。尽管土壤对我们这个星球及其60亿人口的生计很重要，但我们对风化的了解是有限的。这是因为不同的科学方法没有充分地结合起来，以应对发生的许多复杂的相互作用。因此，需要一个多学科的方法来研究土壤形成的速率和过程。土壤真菌似乎利用植物能量从岩石中提取养分--但涉及的机制尚不确定。我们想知道生物风化是否是由植物光合作用产生的糖流驱动的，以换取矿物质颗粒中的营养元素(如磷、钾)。林木产生的总化学能(糖)的近三分之一直接传递给共生(互惠)的根部真菌。这些真菌完全覆盖了树根，并在土壤中形成了广泛的活丝网。实际上，树木吸收的所有营养都是通过这些真菌吸收的。这项研究计划将确定真菌细胞及其分泌物如何与矿物表面相互作用，并影响从矿物到有机体的营养转移速度。将生物过程作为分子水平上理解矿物如何溶解的核心，这与现有的理论背道而驰。研究生物系统中这些基本的分子风化机制使我们能够创造新的概念和数学模型来描述生物风化，并用于土壤风化动力学的计算机模拟。我们建议在三个观察水平上研究这些生化相互作用：1.在分子尺度上了解活细胞和矿物之间的相互作用并量化分解矿物结构的化学物质；2.在土壤颗粒尺度上量化真菌、根和其他生物(如细菌)的活动和空间分布及其对矿物溶解释放养分速率的影响；3.在土壤剖面尺度上测试活性真菌和碳能的空间分布及其季节变异性和对矿物溶解速率的影响的模型。我们将结合多个科学领域的专业知识。生物学家将在存在和不存在作为营养来源的矿物质的情况下与真菌和植物培养物合作，并测量真菌网络中的碳能量通量。表面化学家将使用与细胞和矿物表面相互作用的X射线和红外线光束，然后使用复杂的传感器进行测量，以提供可能形成的化学键的信息。物理学家将测量真菌细胞和矿物表面之间的微小作用力，但确定真菌是否真的附着并形成化学键。材料科学家将使用高度专业化的可视化方法，在几乎原子尺度上观察溶解矿物的形状和组成。地球化学家将研究矿物如何随时间变化，以及有多少矿物被溶解。通过从几乎分子到土壤剖面尺度的工作所获得的数据和理解，将被数值建模人员用来模拟高等植物、真菌、矿物、土壤有机质和渗入水之间的复杂相互作用。最后一步是模拟气候条件和土壤管理变化的一系列情景下的土壤剖面风化。预期的成果是对土壤形成，特别是生物风化的作用有了更深入的基本了解，以便我们能够改进对这一重要自然资源的管理策略。

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 multidisciplinary 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 weathering 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.