CHEMISTRY AND BIOAVAILABILITY OF ORGANIC MATTER ADSORBED ON SOIL MINERAL SURFACES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1006594
• Project Start Date: Oct 1, 2015
• Project End Date: Sep 30, 2020
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF MAINE
(N/A)
ORONO,ME 04469

Performing Department
School of Food and Agriculture

Non Technical Summary
The use of atomic force microscopy and ultrahigh resolution mass spectrometry will allow the examination of the chemical mechanisms by which organic matter interacts with both soil solutions and on soil mineral surfaces to stabilize SOM which is necessary to maintain and increase soil health and quality. The use of organic matter derived from sources typically utilized in sustainable management practices in studies under controlled laboratory settings allows us to explore the ways in which the mineral surface chemical properties and the chemical composition of organic matter combine to control processes observable at the field-scale. The studies will build on a modern understanding of SOM by examining the chemistry of labile, soluble fractions of organic matter and how the configuration of adsorbed organic matter affects its susceptibility to microbial decomposition.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0110	2000	100%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
2000 - Chemistry;

Keywords

chemical force spectroscopy

ion cyclotron resonance mass spectrometry

Goals / Objectives
Molecular-scale chemical information would greatly improve our understanding of the factors that control the bioavailability of SOM and processes that stabilize terrestrial carbon. This study tests the hypothesis that soil carbon sequestration is controlled through surface interactions of organic matter with soil minerals. This will be accomplished by coupling two state-of-the-art chemical techniques [ultrahigh resolution mass spectrometry and atomic force microscopy (AFM)] to elucidate the processes involved in SOM sorption and microbial decomposition reactions at the molecular scale.1. Determine the chemical characteristics of adsorbed soil organic matter using ultrahigh resolution Fourier transform ion cyclotron resonance.2. Determine the affinity of organic matter to soil mineral surfaces using atomic force microscopy.3. Determine the decomposition kinetics of adsorbed organic matter as a function of the chemical composition of the organic matter and bond strength to the mineral surface.

Project Methods
I.Objective 1. Fractionation of DOM upon sorption to mineral surface has been demonstrated through the use of size-exclusion chromatography and spectroscopic analysis (Chorover and Amistadi, 2001; Ohno et al., 2007). ESI-FT-ICR mass spectrometry will be conducted to develop a chemical profile of the pre- and post-sorption DOM components. Analysis of these solutions will provide a more detailed demonstration of the chemical characteristics of the DOM fractions that are preferentially adsorbed by soil minerals than previously reported by our use of the state-of-the-art ultrahigh resolution mass spectroscopy.All ESI-FT-ICR-MS analyses will be conducted with the 12 Tesla Bruker Daltonics Apex Qe FT-ICR-MS housed at the College of Sciences Major Instrumentation Cluster at Old Dominion University. The DOM samples from both pre- and post-sorption will be diluted with LC-MS grade methanol to give a final sample composition of 50:50 (v/v) methanol:water. In order to increase the ionization efficiency, ammonium hydroxide will be added immediately prior to ESI to bring the pH up to 8. Samples will be introduced by a syringe pump providing an infusion rate of 120 mL hr-1 and analyzed in negative ion mode with electrospray voltages optimized for each sample. Previous studies have shown that negative ion mode avoids the complications of the positive ion mode in which alkali metal adducts, mainly Na+, are observed along with protonated ions. Ions (in the range of 200-2000 m/z) will be accumulated in a hexapole for 1.0 sec before being transferred to the ICR cell. Exactly 300 transients, collected with a 4 MWord time domain, will be added, giving about a 30 min total run time per sample. The summed free induction decay signal will be zero-filled once and Sine-Bell apodized prior to fast Fourier transformation and magnitude calculation using the Bruker Daltonics Data Analysis software. Prior to data analysis, all samples will be externally calibrated with a polyethylene glycol standard and internally calibrated with naturally present fatty acids within the sample.A molecular formula calculator developed at the National High Magnetic Field Laboratory in Tallahassee, FL, (Molecular Formula Calc v.1.0 ©NHMFL, 1998) will be used to generate empirical formula matches for the resolved peaks using C (8 to 50 atoms), H (8 to 100 atoms), O (1 to 30 atoms), N (0 to 5 atoms) , S (0 to 2 atoms), and P (0 to 1 atom) as the limiting atomic values. Only m/z values with a signal to noise above 5 will be used in the molecular formula calculator. The resulting formula list will be passed through a MATLAB routine to constrain formulas to chemically feasible formulas. For species with m/z> 400, two or three formula assignments may be listed for a particular m/z value based on a pre-selected error window (0.5 ppm). In these cases, one formula assignment will be selected based on the hierarchy order of Kendrick mass defect, lowest number of N and S atoms, and the lowest deviation between observed and calculated m/z values (Kujawinski et al., 2009; Ohno and Ohno, 2013).Objective 2. AFM analysis will be carried out using an Asylum Reseach MFP-3D instrument equipped with intermittent contact mode and lateral force imaging capabilities. A closed fluid cell system for studying minerals in-situ will allow measurement directly in experimental solutions. In general, force measurements will be conducted in solutions using silicon nitride (Si3N4) cantilever tip. A force profile as a function of the distance between the tip and surface of the mineral is obtained. At each x-y location, the raw force measurement on the cantilever is recorded as the tip is moved along the z-axis. The raw deflection data is converted to a force-distance profile using the spring constant of each cantilever. The measured force profiles are typically model using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) which allows direct determination of the surface charge potential of the mineral surface (Yan et al., 2011). Force profiles of soil mineral surfaces will be determined as a function of SOM surface loading. Two AFM methodologies for the study of DOM sorption on the minerals, one ex-situ and the other in-situ, will be developed and implemented. For the ex-situ method, mineral surfaces with adsorbed DOM will be prepared using the highest OM concentration used in the sorption study described above. After the reaction period, the suspension will be immediately (no centrifugation) vacuum filtered through a 0.4 µm polycarbonate filter. The retained minerals will be air dried in ambient room conditions prior to AFM characterization of the surfaces. A control will consist of the minerals being exposed to a background solution identical to the treatment solutions except for the DOM. Recognizing that complete coverage of the goethite surface by DOM will be undesirable in identifying the most reactive crystal facets and surface sites, we will modify the DOM loading to create fractional surface coverage to clearly distinguish between surface regions of exposed goethite from regions of DOM-coated goethite. The DOM will be readily distinguished from goethite by utilizing phase-contrast imaging in IC-AFM (Brandsch and Bar, 1997). By varying the OM loading, any preferential adsorption to specific facets will be discerned by comparing facet coverage distributions as a function of loading.The in-situ methodology will employ the use of the flow-through fluid AFM cell. In these experiments, goethite crystals will be affixed to mica surfaces using a procedure outlined in previous clay mineral AFM studies (Bosbach et al., 2000; Bickmore et al., 2001). DOM-free solutions as the control will be initially passed through the fluid cell in order to establish the goethite particle morphologies. By carefully switching the fluid composition to the DOM-containing solutions using a fluid delivery system, we will image the same set of particles during the process of DOM adsorption. In this way, we will monitor, in real time, the accumulation of DOM at the goethite-water interface, providing a ranking of the rates of DOM uptake on different crystal facets.Objective 3. We will use the data from the sorption experiments to guide how much DOM solution and mineral will be needed to obtain ~5 mg of adsorbed C per incubation unit. The incubation study is based on the protocol of Mikutta et al. (2007) and Schneider et al. (2010). The minerals retained on the filter(s) will be washed with DI-H2O (1:200, w:v) and transferred to 60-mL glass serum bottles which will provide the decomposition kinetics of adsorbed DOM. Decomposition of the identical quantity of carbon will be used to determine the decomposition kinetics of the DOM. Thirty mLs of a nutrient solution containing 0.4 mg N, 0.3 mg P, and 0.8 mg K will be added. Thirty µL of a fresh field soil extract (1:10, soil:deionized-H2O) will be added to each bottle to provide a microbial population representative of fresh field soils. The flasks will be sealed with a septum cap and incubated in the dark at 20° C for 60 days to determine the kinetics of organic matter decay (Craine et al., 2010). Flasks will be prepared in triplicate. The CO2 concentration in the headspace will be measured at days 0, 2, 4, 6, 10, 15, 20, 30, 40, and 60 using a LI-COR LI-7000 gas chromatograph. The cumulative CO2 evolved is fit using the double exponential model:Ct = C1[1 - exp(-k1t )] + C2[1 - exp(-k2t )]where C1 and C2 are the size of the labile and stable carbon pools, respectively, and k1 and k2 are their respective decomposition rate constants (Mallory and Griffin, 2007).The use of the chemical characterizations from the ultrahigh resolution mass spectrometry can be used to infer how the decomposition kinetics of OM is affected by the chemical characteristics of the DOM.

Progress 10/01/15 to 09/30/20

Outputs
Target Audience:The target audience for this project includes the ecological and environmental scientific community involved with soil organic matter and climate change issues. Our results provide a better chemical understanding of the factors involved in the adsorption of acidic organic molecules to inorganic iron (oxy)hydroxide mineral surfaces that plays a key role in many important terrestrial and aquatic ecosystem processes. Thus, the studies will add to the knowledge required to better adapt our management of systems in the face of a changing climate. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?With the covid-19 pandemic, planned presentations at the American Chemical Society, Soil Science Society of America, and Clays and Clay Mineral Society national meetings were canceled. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? We have continued to use density functional theory to better describe the bonding between soil organic matter model molecules with iron oxide mineral surfaces. Our focus this year has been to better understand the solvation effects on modeling the non-covalent bonding interactions.

Publications

• Type: Journal Articles Status: Published Year Published: 2019 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2020 Citation: 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.

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:The target audience for this project include the ecological and environmental scientific community involved with soil organic matter and climate change issues.Our results provides a better chemical understanding of the factors involved in the adsorption of acidic organic molecules to inorganic iron (oxy)hydroxide mineral surfaces that plays a key role many important terrestrial and aquatic ecosystem processes. Thus, the studies will add to the knowledge required to better adapt our management of systems in the face of a changing climate. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?We have been publishing our results in peer-reviewed manuscripts, as well as presenting our work at conferences and symposia (see listing below). Coward, E., T. Ohno, and D.L. Sparks. Kinetic structuring: Temporal molecular fractionation of organic matter during mineral adsorption. Soil Sci. Soc. Am. National Meeting, San Diego, CA, Jan. 6-9, 2019. Ohno, T., M.S. Erich, and J.D. Kubicki. Adsorptive interaction of phosphate and model root exudates with goethite: Coupling experiment with density functional theory. Soil Sci. Soc. Am. National Meeting, San Diego, CA, Jan. 6-9, 2019. Plante, A.F., E.K. Coward, S. Kim, and T. Ohno. Soil organic matter-mineral associations as a microbial substrate selection engine. Am. Geophys. Union Meeting, Washington, D.C., Dec. 10-14, 2018. Kubicki, J.D., J. Guo, L. Ma, P.G. Hatcher, and T. Ohno. Modeling competitive adsorption of phosphate and salicylate on the goethite (210) surface. Am. Geophys. Union Meeting, Washington, D.C., Dec. 10-14, 2018. Kubicki, J.D., J. Guo, L. Ma, T. Ohno, and P.G. Hatcher. Modeling competitive adsorption of phosphate and salicylate on the goethite (020) surface. 130th Geol. Soc. Am. National Meeting, Indianapolis, IN, Nov. 4-7, 2018. Kubicki, J.D., J. Guo, L. Ma, T. Ohno, and P.G. Hatcher. Modeling competitive adsorption of phosphate and salicylate on the goethite (010) surface. 256th Am. Chem. Soc. National Meeting, Boston, MA, Aug. 19-23, 2018. Coward, E., T. Ohno, and D.L. Sparks. Kinetic structuring: Temporal molecular fractionation of organic matter during mineral adsorption. Goldschmidt Conference, Boston, MA, Aug. 12-17, 2018. What do you plan to do during the next reporting period to accomplish the goals?We will continue with our density functional theory calculations to characterize the ground state electronic structure of the organic matter molecules adsorbed onto goethite minerals. In addition, we are going to use computational molecular dynamics simulations to better understand the temporal and spatial scaffolding of the adsorbed organic matter that we are observing in our experimental studies.

Impacts
What was accomplished under these goals? We have continued our work within the third major goal to apply density functional theory to better understand the interaction of soil organic matter with mineral surfaces because it is a critical reaction involved in many ecosystem services, including stabilization of carbon in the terrestrial carbon pool and bioavailability of plant nutrients such as phosphorus. From a comparative study of different functionals and basis sets, we have selected the B3LYP functional and the 6-31++G(d,p) basis set to use in our computations to directly calculate the bond strengths of both the covalent bond between the carboxyl group of organic matter molecules and the iron atom of the mineral being innvestigated. The functional and basis set together define the mathematical equations used to model the quantum mechanical wavefunction of the studied system, in this case the organic matter molecule adsorbed onto the mineral surface. Additional criteria selected were the use of the Grimme D3 dispersion function to model van der Waals forces in our calculations. Topological determination of electron density at critical bond points using quantum theory of atoms in molecules (QTAIM) analysis revealed that the presence of multiple bonding paths between the organic acid and the FeOOH cluster is essential in determining the competitive adsorption of organic acids and phosphate for FeOOH surface adsorption sites. The electron density and Laplacian parameter values from QTAIM indicated that the primary carboxylate - FeOOH bond was more ionic than covalent in nature. The experimental and computational results provide molecular-level evidence of the important role of electrostatic forces in the bonding between acidic organic molecules with inorganic mineral surfaces. This knowledge may assist in the formulation of management studies to meet the challenges of maintaining ecosystems services in the face of a changing climate.

Publications

• Type: Journal Articles Status: Published Year Published: 2019 Citation: 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.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:Researchers interested in soil biogeochemistry of carbon and phosphorus. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?We have presented the results of our study at national society meetings of the: American Chemical Society, Soil Science Society of America, Goldschmidt Conference, American Geological Society, and Association of Geophysical Union. What do you plan to do during the next reporting period to accomplish the goals?Continue with the computational and ultrahigh resolution mass spectrometry work to gain a better understanding of how soil phosphorus and carbon react in soil systems.

Impacts
What was accomplished under these goals? We have used density functional theory (DFT) and quantum chemical topography (QCT) analysis to develop a better understanding of the adsorption of eight plant metabolites and phosphate with a Fe (oxy)hydroxide mineral surface. We have also experimentally determined the adsorption of the metabolite molecules and phosphate onto the mineral to evaluate if calculated molecular chemical properties relate to the experimentally determined extent of adsorption. The use of DFT and QCT analysis can provide atomic level mechanistic details of agroecosystem-relevant reactions that are impossible, or very difficult, to obtain experimentally. The use of computational chemistry promises to provide insight into how the interaction of plant metabolites and phosphate for adsorption onto mineral surfaces affects their bioavailability and stability.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.
• Type: Journal Articles Status: Published Year Published: 2018 Citation: 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.

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Researchers interested in organic matter chemistry. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?Attending the 2017 Soil Science Society of America Annual Meeting in Tampa, Florida. What do you plan to do during the next reporting period to accomplish the goals?Continue with the ultrahigh resolution mass spectrometry characterization of organic matter.

Impacts
What was accomplished under these goals? Plant biomass is the primary source material for the formation of soil organic matter, which comprises the largest terrestrial pool of the global C cycle. Adsorption of water-extractable organic matter (WEOM) to soil mineral surfaces is a critical step in the process of organic matter accumulation. In this study, we examined the molecular fractionation of WEOM derived from field-grown corn, wheat, and soybean crop residues upon adsorption to iron (oxy)hydroxide (FeOOH) mineral using ultrahigh resolution mass spectrometry. The results show that aromatic, N-containing aliphatic as well as lignin-like molecules with higher O/C atomic ratios have preferential affinity for FeOOH surfaces. Lignin-like molecules with low and high numbers of O atoms were adsorbed, while those with intermediate O numbers were not adsorbed. This pattern is likely due to two different mechanisms of adsorption that is dependent on molecular size: smaller molecules with low O numbers bond through an inner-sphere ligand exchange mechanism, and the larger molecules with high O numbers bond through the formation of multiple H-bonds between the WEOM and FeOOH surface functional groups. Adsorption of WEOM to soil mineral surfaces has wide ecosystem implications, since adsorbed organic matter molecules are now believed to be more protected from microbial decomposition reactions. This study shows that WEOM chemical composition is an important factor controlling its adsorption to mineral surfaces. Understanding these soil and crop chemical interactions at the molecular level will be increasingly important for developing production systems that maintain high SOM levels and soil health in the decades ahead.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Ohno, T., K.A. Heckman, A.F. Plante, I.J. Fernandez, T.B. Parr. 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.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Researchers interested in soil organic matter chemistry. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?Publication in peer reviewed journals. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Demostrated expanded analytical window with positive mode electrospray ionization.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Chasse, Alexander W. and Ohno, Tsutomu. Higher Molecular Mass Organic Matter Molecules Compete with Orthophosphate for Adsorption to Iron (Oxy)hydroxide. ENVIRONMENTAL SCIENCE & TECHNOLOGY Volume: 50 Issue: 14 Pages: 7461-7469
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Comparative study of organic matter chemical characterization using negative and positive mode electrospray ionization ultrahigh-resolution mass spectrometry. Ohno, T (Ohno, Tsutomu)[ 1 ] ; Sleighter, RL (Sleighter, Rachel L.)[ 2 ] ; Hatcher, PG (Hatcher, Patrick G.)[ 2 ] ANALYTICAL AND BIOANALYTICAL CHEMISTRY Volume: 408 Issue: 10 Pages: 2497-2504