The Geochemical Carbon Cycle: A Vadose-Hydrologic Study of the Effect of Plants on Weathering

9508003 Keller二氧化碳（CO2）是一种温室气体。了解大气CO2浓度与气候关系的一个途径是研究长时间尺度上影响大气CO2的过程。CO2从地球大气层长期转移到地壳的主要途径是土壤、底土和地下水系统中常见矿物的“化学风化”，随后溶解的物质通过大陆排水系统输送到海洋，沉积在海底。这种顺序影响CO2的转移，因为矿物溶解消耗含CO2的酸，夹带碳酸氢盐，沉积碳酸盐矿物。埋藏碳酸盐矿物中的CO2通过火山作用和变质作用返回大气。这些过程的相对速率决定了任何时候大气和岩石圈中二氧化碳的质量，并在此过程中影响地球的气候。因此，重要的是控制循环中各种过程的速率的因素。植物群落是一个重要因素。植物可以通过提高地下酸的浓度，促进新鲜矿物表面的暴露，并将矿物颗粒结合到土壤的保水结构中来增强化学风化。然而，由于难以将其他变量从比较性实地研究中排除，因此对这些机制的风化增强的实际程度知之甚少。这项研究利用了正在进行的植物养分循环的长期，田间规模的实验。收集所需的数据，为后续的研究，以测试假设的植物风化关系。现有的仪器将得到加强，以观察各种植物群落下土壤和底土中化学风化如何随深度和时间而演变

9508003 Keller Carbon dioxide (CO2) is a greenhouse gas. One avenue to understanding the relationship of atmospheric CO2 concentration to climate, is to study processes affecting atmospheric CO2 on long time scales. The principal pathway for long-term transfer of CO2 from Earth's atmosphere to its crust is "chemical weathering" of common minerals in soils, subsoils, and groundwater systems followed by transport of the dissolved material to the oceans in continental drainage, where they are deposited on ocean floor. This sequence effects transfer of CO2 because mineral dissolution consumes CO2 containing acids, entrains bicarbonate, deposits carbonate minerals. CO2 in buried carbonate minerals returned to the atmosphere by volcanism and metamorphism. The relative rates of these processes determine the masses of CO2 in the atmosphere and lithosphere at any on time and, in the process, affect Earth's climate. It is therefore important the factors controlling the rates of the various processes in the cycle. Plant communities, are an important factor. Plants could enhance chemical weathering by raising subsurface concentrations of acids, facilitating the exposure of fresh mineral surfaces, and binding mineral grains into water-retaining structures characteristic of soils. The actual extent of weathering enhancement by these mechanisms is, however poorly understood because of the difficulty of factoring other variables out of comparative field studies. This study takes advantage of ongoing long-term, field-scale experiments in plant nutrient cycling. To collect needed data for subsequent research to test hypotheses on plant-weathering relationships. Existing instrumentation will is augmented to observe how chemical weathering evolves with depth and time in soils and subsoils beneath various plant communities