An Integrated Wet Chemical and TEM Investigation of Organic Acid Promoted Phosphate Dissolution in Ferrihydrite-Boehmite Mixtures.

The goal of this study is to investigate organic acid promoted dissolution of phosphate in binary mixtures of ferrihydrite and boehmite. Ferrihydrite and boehmite are poorly crystalline analogs of Fe- and Al-oxyhydroxides respectively in soils and considered to be the main P sorbents in acid soils. Because organic acid anions citric, malic, and gluconic released by plant roots or microbes are considered to be the main mode of P solubilisation in soils, this biogeochemical research is pertinent to improving soil fertility. Our understanding of phosphate dissolution comes from studies conducted in soils and minerals with or without plants as a means of phosphate uptake. The results from these studies are difficult to interpret due to the complicating influence of metabolism as in microbial cells or plants or due to re-distribution of phosphate on mineral surfaces upon dissolution. Here, we will characterize phosphate dissolution in the presence of a high affinity transporter for yeast cells (PHO84) reconstituted into proteoliposomes (henceforth referred to as PPL) functioning as a sink for dissolved phosphate. The specific objectives of this study are to characterize citric, malic, and gluconic acid promoted phosphate dissolution in single mineral systems of ferrihydrite and boehmite and binary mixtures of ferrihydrite and boehmite as a function of pH (4, 6, 9), organic acid type (as in number of carboxylic acid groups), organic acid concentration (50 µM concentration found in soils vs. 10 mM estimated at root tips), and time in the presence and absence of PPL. The concentration of dissolved phosphate, Fe, and Al measured in single-mineral and binary mixtures along with TEM (transmission electron microscopy) images pre- and post-dissolution will be presented and will provide information on mineral interactive effects on P dissolution in binary mixtures.