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Richardson JA, Kim H, Kas JJ, You X, Andersen A, Ginovska B, Bhattacharjee A, Sarangi R. X-ray absorption spectroscopy and theoretical investigations of the effect of extended ligands in potassium organic matter interaction. J Chem Phys 2024; 160:044114. [PMID: 38284657 DOI: 10.1063/5.0183603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 01/07/2024] [Indexed: 01/30/2024] Open
Abstract
Potassium (K) is an essential nutrient for plant growth, and despite its abundance in soil, most of the K is structurally bound in minerals, limiting its bioavailability and making this soil K reservoir largely inaccessible to plants. Microbial biochemical weathering has been shown to be a promising pathway to sustainably increase plant available K. However, the mechanisms underpinning microbial K uptake, transformation, storage, and sharing are poorly resolved. To better understand the controls on microbial K transformations, we performed K K-edge x-ray absorption near-edge structure (XANES) spectroscopy on K-organic salts, including acetate, citrate, nitrate, oxalate, and tartrate, which are frequently observed as low molecular weight organic acids secreted by soil microbes, as well as humic acid, which acts as a proxy for higher molecular weight organic acids. The organic salts display feature-rich K XANES spectra, each demonstrating numerous unique features spanning ∼13 eV range across the absorption edge. In contrast, the spectra for humic acid have one broad, wide feature across the same energy range. We used a combination of time-dependent density functional theory and the Bethe-Salpeter equation based approach within the OCEAN code to simulate the experimental spectra for K-nitrate (KNO3) and K-citrate [K3(C6H5O7)·H2O] to identify the electronic transitions that give rise to some of the outlying and unique spectral features in the organic salts. KNO3 has both the lowest and highest lying energy features, and K3(C6H5O7)·H2O is produced by several soil microbes and is effective at mineral weathering. Our results analyze the K-organic salt bonding in detail to elucidate why the spectral shapes differ and indicate that the K K-edge XANES spectra are associated with the entire ligand despite similar first-shell bonding environments around the K center. The improved understanding of K bonding environments with organic ligands and their use for interpretation of the K-XANES spectra provides an important toolkit to understand how K is transformed by microbial processes and made bioavailable for plant uptake.
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Affiliation(s)
- Jocelyn A Richardson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Hoshin Kim
- Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99354, USA
| | - Joshua J Kas
- Department of Physics, University of Washington Seattle, Box 351560, Seattle, Washington 98195, USA
| | - Xiao You
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Amity Andersen
- Environmental Molecular Sciences Division, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, 3335 Innovation Blvd., Richland, Washington 99354, USA
| | - Bojana Ginovska
- Physical Sciences Division, Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington 99354, USA
| | - Arunima Bhattacharjee
- Environmental Molecular Sciences Division, Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, 3335 Innovation Blvd., Richland, Washington 99354, USA
| | - Ritimukta Sarangi
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
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