A Molecular Examination of Agriculturally-Derived Lignin Oxidation

Title

A Molecular Examination of Agriculturally-Derived Lignin Oxidation

College

College of Sciences

Program

Ph.D. Chemistry

Publication Date

3-28-2019

Abstract

Fertilizers are utilized in agriculture to increase crop yields, but the over application of phosphate fertilizers is resulting in excess nutrients in the soil. As a result, phosphate is becoming less available for plants as it is lost to agricultural runoff. In addition to fertilizer input, agricultural land receives large carbon inputs in the form of biomass. After harvesting, biomass from crop residues are incorporated into the soil, slowly degrading through the soil horizon, leaving lignin as the major biopolymer. As a significant contributor to soil organic matter, lignin and its degradation products play an important role in soil dynamics. The interaction between these degradation products and phosphate can impact the bioavailability of the nutrients for the plants, thus altering the crop yield for future growing seasons. Studies have shown that phosphate availability is largely controlled by iron and aluminum hydroxides, which occurs through a two-step sorption process, while lignin has been shown to irreversibly sorb to iron hydroxides due to the presence of phenolic groups. Little research has been done regarding the interaction between lignin and phosphate at the mineral surface. These interactions are believed to play a large role in the bioavailability of phosphate. This research focuses on how the lignin component of organic matter interacts with phosphorus on the surface of minerals after degradation. Lignin was isolated from field-grown corn biomass, and quantified using solid-state 13C NMR. Samples were exposed to hydroxyl radicals and characterized using FTICR-MS. Oxidation occurred in both above- and below-ground lignin, which resulted in slightly different elemental compositions. The ultimate goal is to determine the mechanisms by which nutrients interact with soil organic matter at mineral surfaces, which will help determine how to maximize crop yield while reducing the over- or under-application of phosphate fertilizers.

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A Molecular Examination of Agriculturally-Derived Lignin Oxidation


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