Intellectual merit: The latest terrestrial N cycle paradigm considers soluble organic nitrogen (SON) as a rate limiting step for regulating the overall N availability in ecosystems. Our lack of understanding of the micro-scale processes/mechanisms of interactions between soil minerals and SON compounds hinders our ability to predict N flux between different soil compartments at the ecosystem-scale. To address this issue, an interdisciplinary approach that combines a broad array of novel molecular, biological, and synchrotron-based spectroscopic techniques is proposed to investigate the interaction mechanisms between soil minerals and amino acids and small peptides, two key components of soil SON. Novel methods will be used to achieve the research. The phage display technique will be used to screen, in a short period of time, billions of random small peptide sequences for those peptides displaying a selective affinity for a particular mineral surface. Macro-scale adsorption isotherms for amino acids and small peptides on four minerals commonly found in soil will be obtained. Using the samples collected from the adsorption isotherms experiment, polarization-dependent N (1s) near-edge x-ray absorption fine structure (NEXAFS) will be used to investigate, at micro-scale, the average molecular surface orientation. Lastly, a microbial essay method will be used to understand at micro-scale how molecular surface organization on mineral surfaces affects the microbial utilization of adsorbed amino acids and small peptides.
Broader impacts: The PIs are cooperating with two local high schools (The Mississippi School for Mathematics and Science and The West Oktibbeha County High School) to recruit future minority undergraduate students for summer research projects. Those summer research projects will provide minority high school students opportunities to gain hands?]on experience in biogeochemistry research and state of the art instrumentations, to obtain insight into the nature of both undergraduate and graduate school, to work with university professors and graduate students as an interdisciplinary team, and to have informed choices about how to advance their future career. The students will also be given the opportunity to attend regional or national meetings and to visit national laboratories. The work from these students and the research of this proposal will be showcased at their high schools and highlighted in state competitions such as the Engineering Fair and the Young Scientist Division at the Mississippi Academy of Science.
Up to date, terrestrial C and N models have focused mainly on total C and N flux between broadly defined labile and recalcitrant soil pools. Organo-mineral interactions play a key role in the flux of C and N between the soluble and mineral-associated stabilized organic C and N pools in soils, and thus regulate the bioavailability of soil organic matter to microorganisms and plants. Mineral-facilitated organic matter accrual with soil development has been observed but further verification of organic C and N speciation during this accrual process is needed across a number of ecosystems. We found strong synchrotron-based spectroscopic evidence of preferential accrual of peptides/proteins over other organic nitrogen compounds associate with soil minerals in there independent undisturbed ecosystems developed across 4000, 20,000, and 60,000-year chronosequences. The result from this investigation strongly support that peptide/protein-mineral interaction plays an important role in affecting terrestrial N cycle. We have found that the mineral-associated organic C consists of four major species: aromatic-C, phenolic-C, aliphatic-C, carboxylic-C, and O/N-alkyl-C. The mineral-associated organic C speciation composition varied significantly during the soil development for all 3 independent soil chronosequences. Relative content of aromatic-C decreased and relative content of aliphatic-C increased in the mineral-associated organic matter during soil development. Relative content of O/N-alkyl-C in the mineral associated organic matter increased within the first 100-200 years of soil development and reached to a stable state thereafter, while the change of relative content of carboxylic-C with soil development displayed different trend among the chronosequences. The results from this investigation suggest continuous mineral-sequestration and stabilization of aliphatic-C and O/N-alkyl-C compounds during soil development, while the aromatic-C compounds associated with soil minerals were continuously transformed into other C species. This project has trained one Postdoctoral Researcher with analytical skills on phage display techniques. It has provided her with experience on designing and conducting independent research and synthesizing experiment results for presentation and publication. A graduate student has been trained at two state-of-the-art international research facilities to utilize synchrotron-based X-ray absorption spectroscopy for research on C and N biogeochemistry. Two talks and one poster were presented at the annual meeting of the Soil Science Society of America in November 2012. Two meeting abstracts have been submitted to the 2013 Soil Science Society of America.
