Title: Professor Emeritus of Soil Chemistry
Degree: Ph. D. 1983, Cornell University
Location: 108 Deering Hall
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Professional Interests: Organic matter chemistry, computational chemistry, ion cyclotron mass spectrometry
Teaching: PSE 469 Soil Microbiology, PSE 580/581 Scientific Communication I/II
Iron (Fe)-bearing minerals, with their preponderance of surface hydroxyl groups play a critical role in biogeochemical processes such as the adsorption of organic matter (OM). The formation of Fe-associated organic matter is now known to be a critical factor in the stabilization of carbon (C) in soils. The changing global climate is causing intensification of rainfall, with global average maximum daily rainfall increases of 5.9 – 7.7% per °C of warming. This increase affects the stabilization of soil C because greater precipitation favors soil Fe reduction. Anaerobic conditions can drive the reductive dissolution of soil Fe(III) (oxyhydr)oxide minerals through predominately biotic processes that results in the release of aqueous Fe(II) cations and previously-adsorbed OM to soil solution. Upon re-introduction of O2 into the anoxic soil as it dries, Fe(II) will be oxidized leading to re-precipitation of Fe(III) (oxyhydr)oxide, which can re-stabilize the OM. Rainfall intensification combined with higher global temperatures, will result in increased wet-dry soil cycling and repeated release and stabilization of soil OM in the future.
OM interactions with mineral surfaces are dynamic and sensitive to interfacial energies and topology. I have used ultrahigh resolution electrospray ionization – ion cyclotron resonance – mass spectrometry to show that soil OM molecules exhibit temporal molecular fractionation at Fe (oxyhydr)oxide interfaces. This temporal fractionation leads to a ‘zonal’ assembly of OM at the mineral interface and results in a spatially diverse scaffolding architecture for different classes of OM molecules. The chemical details of the interaction of soluble OM with mineral surfaces remain unclear. While the formation of covalent bonds via ligand exchange has been frequently assumed for OM-mineral bonding, my density functional theory calculations using electron density data have shown that the bonds involved in the complexation between model OM ligands and Fe nano-clusters are more electrostatic than covalent.
Molecular dynamics (MD) simulations can provide chemical insight into the interactions (electrostatic and non-ionic van der Waals dispersion forces) between iron nanoclusters with OM molecules and inorganic ions typically present in soil solutions. Modeling aggregation processes requires large-scale MD simulations that generate large and complex data sets of high spatiotemporal resolution, making the extraction of useful information a challenging task. Aggregation dynamics are inherently challenging to characterize, with numerous, intermediate metastable structures. My current goal is to show that machine learning (ML) can assist in the analysis of MD simulation data to explore the effects of OM chemical characteristics on aggregation dynamics of Fe nanoparticles.
This work will bring this powerful artificial intelligence approaches to climate change mitigation research. ‘Natural climate solutions’, including increasing levels of soil organic matter to sequester soil C, are being emphasized at the federal and state levels, including in the 2020 Climate Action Plan, Maine Won’t Wait, released by Governor Mills. Although policies are being proposed to increase soil C sequestration in terrestrial ecosystems, including agricultural and forested lands, many questions remain about the effectiveness of this practice in slowing the rate of atmospheric CO2 increase. In particular, long-term stability of sequestered C under changing environmental conditions is unclear. This work addresses this question.
Recent Publications [available through ResearchGate]:
T. Ohno, and J.D. Kubicki. 2020. Adsorption of organic acids and phosphate to an iron (oxyhydr)oxide mineral: A combined experimental and density functional theory study. J. Phys. Chem. A. 124:3249-3260.
Laffely, A., M.S. Erich, and T. Ohno. 2020. Soluble carbon composition controls rate of CO2 release from rewetted soil. Soil Sci. Soc. Am. J. 84:483-493.
Kubicki, J.D., and T. Ohno. 2020. Integrating density functional theory modeling with experimental data to understand and predict sorption reactions: Exchange of salicylate for phosphate on goethite. Soil Syst. 4:27. //doi.org/10.3390/soilsystems4020027
Ohno, T., N.J. Hess, and N.P. Qafoku. 2019. Current understanding of the use of soil alkaline extractions to understand environmental processes. J. Environ. Qual. 48:1561-1564.
Coward, E.K., T. Ohno, and D.L. Sparks. 2019. Direct evidence for temporal molecular fractionation of dissolved organic matter at the iron oxyhydroxide interface. Environ. Sci. Technol. 53:642-650.
Ohno, T., and G.M. Hettiarachchi. 2018. Soil chemistry and the One Health Initiative: Introduction to the special section. J. Environ. Qual. 47:1305-1309.
Caricasole, P., P.G. Hatcher, and T. Ohno. 2018. Biodegradation of crop residue-derived organic matter is influenced by its heteroatomic stoichiometry and molecular composition. Appl. Soil Ecol. 130:21-25.
Patel, K., C. Tatariw, J.D. MacRae, T. Ohno, S.J. Nelson, and I.J. Fernandez. 2018. Soil C and N responses to snow removal and concrete frost in a northern coniferous forest. Can. J. Soil Sci. 98:436-447.
Ohno, T., R.L. Sleighter, and P.G. Hatcher. 2018. Adsorptive fractionation of corn, wheat, and soybean crop residue derived water-extractable organic matter on iron (oxy)hydroxide. Geoderma 326:156-163.
Chase, A.J., M.S. Erich, and T. Ohno. 2018. Bioavailability of phosphorus on iron (oxy)hydroxide not affected by soil amendment-derived organic matter. Agric. Environ. Lett. 3:170042.
Coward, E., T. Ohno, and A. Plante. 2018. Adsorption and molecular fractionation of dissolved organic matter on iron-bearing mineral matrices of varying crystallinity. Environ. Sci. Technol. 56:1036-1044.
Ohno, T., K.A. Heckman, A.F. Plante, I.J. Fernandez, T.B. Parr. 2017. 14C mean residence time and its relationship with thermal stability and molecular composition of soil organic matter: A case study of deciduous and coniferous forest types. Geoderma 308:1-8.
Chassé, A.W. and T. Ohno. 2016. Higher molecular mass organic matter molecules compete with orthophosphate for adsorption to iron (oxy)hydroxide. Environ. Sci. Technol. 50:7461-7469.
Ohno, T., R.L. Sleighter, P.G. Hatcher. 2016. Comparative study of organic matter chemical characterization using negative and positive mode electrospray ionization ultrahigh resolution mass spectrometry. Anal. Bioanal. Chem. 408:2497-2504.
Boeira de Oliveira, C.M., M.S. Erich, L.C. Gatiboni, T. Ohno. 2015. Phosphorus fractions and organic matter chemistry under different land use on humic Cambisols in Southern Brazil. Geoderma Region. 5:140-149.
Chassé, A.W., T. Ohno, S.R. Higgins, A. Amirbahman, N. Yildirim, and T.B. Parr. 2015. Chemical Force Spectroscopy Evidence Supporting the Layer-by-Layer Model of Organic Matter Binding to Iron (oxy)Hydroxide Mineral Surfaces. Environ. Sci. Technol. 49:9733-9741.
Parr, T.B., C.S. Cronan, T. Ohno, S.E.G. Findlay, S.M.C. Smith, and K.S. Simon. 2015. Urbanization changes the composition and bioavailability of dissolved organic matter in headwater streams. Limnol. Oceanogr. 60:885-900.
Parr, T.B., T. Ohno, K.S. Simon, C.S. Cronan. 2014. comPARAFAC: A library and tools for rapid and quantitative comparison of dissolved organic matter components resolved by PARAFAC analysis. Limnol. Oceanogr. Methods. 12:114-125.