Organic Acid Promoted Dissolution of Phosphate as Affected by its Solid State Speciation in Single and Mixed Fe, Al, Ca Mineral Systems: Implications for Phosphorus Bioavailability

智力优势：目前对有机酸介导的磷酸盐溶解的理解受到缺乏其固态形态的分子尺度表征的限制。此外，磷酸盐溶解还没有在其吸收的背景下进行研究，而没有微生物细胞或植物中代谢的复杂影响。我们目前的知识主要可以归因于土壤中的湿化学研究，其固有的复杂性使得难以表征主要环境变量（pH值，磷酸盐浓度，有机酸类型及其浓度）的影响。此外，磷酸盐溶解在二元和三元混合物的铁，铝和钙矿物（磷酸盐的主要吸附剂），可以作为一个有效的模拟土壤还没有被调查。基于Fe氧化物和Aloxide矿物或含Ca矿物的1：1（按质量计）二元混合物中磷酸盐吸附的基于分子尺度XANES的研究，我们现在可以：1）量化二元和三元混合物中各个矿物相之间的磷酸盐分布（Khare等人，2004; Beauchemin等人，2003）; 2）区分单一矿物和二元混合物中的吸附和表面沉淀（Khare等人，2005）;和3）确定磷酸盐键合构型并区分表面复合物（Khare等人，2007年）。因此，我们现在能够利用这些基于XANES的工具来揭示磷酸盐溶解的分子机制。这项研究将包括一个高亲和力的酵母细胞转运蛋白重组成蛋白脂质体作为一个水槽溶解磷酸盐了解和现实预测磷酸盐溶解在自然系统中。拟议的研究将进行两年多，将解决两个主要假设：假设1：磷酸盐在单矿物、二元和三元混合物中的溶解受固态形态控制假设2：在含Fe和Al矿物的二元混合物中，Al 3+会对磷酸盐的吸收产生不利影响，但在三元矿物体系中，Ca 2+的存在会改善Al的毒性。更广泛的影响：磷是一种重要的植物宏量营养素，也是一种潜在的水污染物。大多数陆地和海洋生态系统是磷有限的，因为磷酸盐矿物是微溶的。由于植物根系或微生物释放的有机酸柠檬酸、苹果酸被认为是土壤和其他自然系统中磷溶解的主要方式，因此基础地球化学研究与提高土壤肥力有关。这一点特别重要，因为粮食生产需要在今后20年翻一番，以维持不断增长的世界人口。表征有机酸介导的磷酸盐在纳米尺度上的溶解也将有助于更好地预测磷的生物利用度和释放。近年来，高磷土壤中磷酸盐的释放已使地表水水质恶化，导致水体富营养化。此外，更好地估计磷酸盐的生物利用度将有助于预测对预测全球变暖至关重要的二氧化碳吸收率。这个项目将有助于研究生的论文，由PI和co-PI共同监督。将采用综合湿化学、光谱（XANES）、显微镜（TEM）和地球化学建模方法。

Intellectual Merit: The current understanding of organic acid mediated phosphate dissolution is limited by the lack of a molecular scale characterization of its solid state speciation. Furthermore, phosphate dissolution has not been studied in context of its uptake without the complicating influence of metabolism as in microbial cells or plants. Our current knowledge can mainly be attributed to wet chemical studies in soils whose inherent complexity makes it difficult to characterize the effect of primary environmental variables (pH, concentration of phosphate, type of organic acid and its concentration). In addition, phosphate dissolution in binary and tertiary mixtures of iron, aluminum and Ca minerals (main sorbents of phosphate) that can serve as an effective analog for soils has not been investigated. Based on a molecular scale XANES based investigation of phosphate sorption in 1:1 (by mass) binary mixtures of Fe-oxide and Aloxide minerals or Ca containing minerals, we can now: 1) quantify the distribution of phosphate between individual mineral phases in binary and ternary mixtures (Khare et al., 2004; Beauchemin et al., 2003); 2) distinguish between adsorption and surface precipitation in single mineral and binary mixtures (Khare et al., 2005); and 3) determine phosphate bonding configuration and differentiate between surface complexes (Khare et al., 2007). Thus, we are now in a position to exploit these XANES based tools in uncovering molecular mechanisms of phosphate dissolution. This research will include a high affinity transporter for yeast cells reconstituted into proteoliposomes as a sink for dissolved phosphate to understand and realistically predict phosphate dissolution in natural systems.The proposed research will take place over two years and will address two main hypotheses:Hypothesis 1: Phosphate dissolution in single mineral, binary and tertiary mixtures is controlled by the solid state speciation (mode of phosphate bonding, adsorption vs. surface precipitation and the partitioning of phosphate in individual mineral phases), of phosphate in these minerals.Hypothesis 2: Phosphate uptake will be adversely affected by Al3+ in binary mixtures of Fe and Al containing minerals however in ternary mineral systems the presence of Ca2+ will ameliorate Al toxicity. Broader Impacts: Phosphorus is an essential plant macronutrient and also a potential water pollutant. Most terrestrial and marine ecosystems are P limited because phosphate minerals are sparingly soluble. Because organic acids citrate, malate released by plants roots or microbes are considered the main mode of P solubilisation in soils and other natural systems, this basic geochemical research is pertinent to improving soil fertility. This is particularly significant because food production needs to double in the next 20 years to sustain increasing world population. Characterizing organic acid mediated phosphate dissolution at the nano scale will also help with better predictions of phosphorus bioavailability and release. Recently phosphate release from heavily fertilized P enriched soils has degraded surface water quality, causing eutrophication. Furthermore, better estimates of phosphate bioavailability will help predict CO2 uptake rates critical to predicting global warming. This project will contribute to a graduate student's dissertation, to be supervised by the PI and co-PI jointly. An integrated wet chemical, spectroscopic (XANES), microscopic (TEM) and geochemical modeling approach will be used.