Effect of Land Use Change on Molecular Composition and Concentration of Organic Matter in an Oxisol.

Land use change from native vegetation to cropping can significantly affect the quantity and quality of soil organic matter (SOM). However, it remains unclear how the chemical composition of SOM is affected by such changes. This study employed a sequential chemical extraction to partition SOM from an Oxisol into several distinct fractions: water-soluble fractions (ultrapure water (W)), organometal complexes (sodium pyrophosphate (PP)), short-range ordered (SRO) oxides (hydroxylamine-HCl (HH)), and well-crystalline oxides (dithionite-HCl (DH)). Coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the impact of land use change on the molecular composition of different OM fractions was investigated. Greater amounts of OM were observed in the PP and HH fractions compared to other fractions, highlighting their importance in SOM stabilization. The composition of different OM fractions varied based on extracted phases, with lignin-like and tannin-like compounds being prevalent in the PP and HH fractions, while aliphatic-like compounds dominated in the DH fraction. Despite changes in the concentration of each OM fraction from native vegetation to cropping, there was little influence of land use change on the molecular composition of OM associated with different mineral phases. No significant selective loss or preservation of organic carbon compounds was observed, indicating the composition of SOM remained unchanged.

Adsorption of Organic Acids and Phosphate to an Iron (Oxyhydr)oxide Mineral: A Combined Experimental and Density Functional Theory Study.

The interaction of soil organic matter with mineral surfaces is a critical reaction involved in many ecosystem services, including stabilization of organic matter in the terrestrial carbon pool and bioavailability of plant nutrients. Using model organic acids typically present in soil solutions, this study couples laboratory adsorption studies with density functional theory (DFT) to provide physical insights into the nature of the chemical bonding between carboxylate functional groups and a model FeOOH cluster. Topological determination of electron density at bond critical 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 carboxylic acids and Fe-hydroxides. 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.

Snowmelt periods as hot moments for soil N dynamics: a case study in Maine, USA.

The vernal transition represents the seasonal transition to spring, occurring as temperatures rise at the end of winter. With rapid snowmelt, microbial community turnover, and accelerated nutrient cycling, this is a critical but relatively under-studied period of ecosystem function. We conducted a study over two consecutive winters (2015-2016) at the Bear Brook Watershed in Maine to examine how changing winter conditions (warming winters, reduced snow accumulation) altered soil nitrogen availability and stream N export during winter and the vernal transition, and how these patterns were influenced by ecosystem N status (N-enriched vs. N-limited). Of the two study years, 2016 had a warmer winter with substantially less snow accumulation and a discontinuous snowpack-and as a result, had a longer vernal transition and a snowpack that thawed before the vernal transition began. Across both years, snowmelt triggered a transition, signaled by increased ammonium concentrations in soil, decreased soil nitrate concentrations due to flushing by meltwater, and increased stream nitrate exports. Despite the contrasting winter conditions, both years showed similar patterns in N availability and export, differing only in the timing of these transitions. The vernal transition has conventionally been considered a critical period for biogeochemical cycling, because the associated snowmelt event triggers physicochemical and biochemical changes in soil systems. This was consistent with our results in 2015, but our data for 2016 show that this may not always hold true, and instead, that warmer, low-snow winters may demonstrate a temporal asynchrony between snowmelt and the vernal transition. We also show that ecosystem N status is a strong driver of the seasonal N pattern, and the interaction of N status and changing climate must be further investigated to understand ecosystem function under our current predicted trajectory of warming winters, declining snowfall, and winter thaw events.

Direct Evidence for Temporal Molecular Fractionation of Dissolved Organic Matter at the Iron Oxyhydroxide Interface.

While the importance of organic matter adsorption onto reactive iron-bearing mineral surfaces to carbon stabilization in soils and sediments has been well-established, fundamental understanding of how compounds assemble at the mineral interface remains elusive. Organic matter is thought to layer sequentially onto the mineral surface, forming molecular architecture stratified by bond strength and compound polarity. However, prominent complexation models lack experimental backing, despite the role of such architecture in fractionated, compound-dependent persistence of organic matter and modulating future perturbations in mineral stabilization capacity. Here, we use kinetic assays and ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry under high temporal frequency to directly detect the molecular partitioning of organic matter onto an iron oxyhydroxide during adsorption. We observed three sequential intervals of discrete molecular composition throughout the adsorption reaction, in which rapid primary adsorption of aromatic compounds was followed by secondary lignin-like and tertiary aliphatic compounds. These findings, paired with observed differential fractionation along formulas nitrogen and oxygen content and decreasing selective sorption with reaction time, support "zonal" assembly models. This work presents direct detection of sequential molecular assembly of organic matter at the mineral interface, an important yet abstruse regulator of carbon stabilization and composition across temporal and spatial scales.

Adsorption and Molecular Fractionation of Dissolved Organic Matter on Iron-Bearing Mineral Matrices of Varying Crystallinity.

Iron (Fe)-bearing mineral phases contribute disproportionately to adsorption of soil organic matter (SOM) due to their elevated chemical reactivity and specific surface area (SSA). However, the spectrum of Fe solid-phase speciation present in oxidation-reduction-active soils challenges analysis of SOM-mineral interactions and may induce differential molecular fractionation of dissolved organic matter (DOM). This work used paired selective dissolution experiments and batch sorption of postextraction residues to (1) quantify the contributions of Fe-bearing minerals of varying crystallinity to DOM sorption, and (2) characterize molecular fractionation using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). A substantial proportion of soil SSA was derived from extracted Fe-bearing phases, and FT-ICR-MS analysis of extracted DOM revealed distinct chemical signatures across Fe-OM associations. Sorbed carbon (C) was highly correlated with Fe concentrations, suggesting that Fe-bearing phases are strong drivers of sorption in these soils. Molecular fractionation was observed across treatments, particularly those dominated by short-range-order (SRO) mineral phases, which preferentially adsorbed aromatic and lignin-like formulas, and higher-crystallinity phases, associated with aliphatic DOM. These findings suggest Fe speciation-mediated complexation acts as a physicochemical filter of DOM moving through the critical zone, an important observation as predicted changes in precipitation may dynamically alter Fe crystallinity and C stability.

Soil Chemistry and the One Health Initiative: Introduction to the Special Section.

Population growth and technical and social changes have always exerted pressure on environmental quality. However, we are experiencing unprecedented change in the rate and scale of human impacts on the environment. The One Health Initiative recognizes that improving the quality of life for humans and other animal species requires a holistic and integrated framework to seek multidisciplinary solutions to global environmental quality challenges. This special section is designed to elucidate the connections among soil health, environmental quality, food safety and security, and human health. Soil chemistry is defined as the field of soil science that deals with the chemical constituents, properties, and reactions of soils. Soil chemistry plays a central role in food production and the protection of human health. Chemical reactions between nutrients or contaminants and soil solids, and the composition of the soil solution and the atmosphere, influence crop growth as well as the quality of our food, air, and water. This collection of nine papers brings together studies that highlight how soil chemical constituents, properties, and reactions can be examined or managed using a multidisciplinary approach to move toward a more efficient, sustainable, nutrient-rich, and low-contaminant food production system that affords protection of soil, water, and human and animal health. We believe that studies such as these are needed to maintain and enhance environmental quality through interdisciplinary scientific approaches for human, animal, and environmental health outcomes.

Higher Molecular Mass Organic Matter Molecules Compete with Orthophosphate for Adsorption to Iron (Oxy)hydroxide.

The competition between orthophosphate and water-extractable organic matter (WEOM) for adsorption to iron (oxy)hydroxide mineral surfaces is an important factor in determining the plant bioavailability of P in soils. Chemical force spectroscopy was used to determine the binding force between orthophosphate and iron (oxy)hydroxide that was coated onto atomic force microscopy (AFM) tips and adsorbed with WEOM. The force measurements were conducted at pH 4.65 and 0.02 M ionic strength which are representative of typical acid soil solutions. The chemical composition of the WEOM was determined by ultrahigh resolution electrospray ionization Fourier transform ion cyclotron mass spectrometry. The results indicate a correlation between aromatic WEOM molecules that are greater than 600 Da and the reduced binding force of orthophosphate to WEOM-adsorbed iron (oxy)hydroxide AFM tips suggesting that the molecular mass of aromatic WEOM molecules plays a critical role in regulating the WEOM-P interactions with surface functional groups of minerals. Based on the results of this study, we show the importance of obtaining a detailed, molecular-scale understanding of soil processes that can help develop better management strategies to reduce waste of limited P resources and adverse environmental impacts. Specifically, soil amendments with greater content of high molecular mass aromatic components may positively affect dissolved P use efficiency in soils by maintaining P in soil solution.

Comparative study of organic matter chemical characterization using negative and positive mode electrospray ionization ultrahigh-resolution mass spectrometry.

The chemical characterization of dissolved organic matter (DOM) is critical for understanding carbon sequestration processes in soils. This work evaluated the use of electrospray ionization in both negative ion mode (ESI-) and positive ion mode (ESI+) for the characterization of DOM extracted from nine terrestrial sources using Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS). The compositing of the peaks from ESI- to ESI+ modes increased the total assigned formulas from 23 to 63 % as compared to the traditional use of ESI- alone for DOM characterization. In general, there was a preferential increase in the number of assignments for the aliphatic and carbohydrate-like DOM components in the ESI+ mode. The soil-extracted DOM specifically exhibited greater increases in the aliphatic and carbohydrate-like DOM components with the combined use of ESI- and ESI+ modes likely due to the greater presence of aromatic DOM molecules that suppressed the ionization of these entities in ESI- mode. On the basis of these findings, we show that improved characterization of DOM is possible through the combined use of ESI- and ESI+ modes for FT-ICR-MS analysis, especially for samples rich in condensed aromatic and aromatic molecules.

Chemical Force Spectroscopy Evidence Supporting the Layer-by-Layer Model of Organic Matter Binding to Iron (oxy)Hydroxide Mineral Surfaces.

The adsorption of dissolved organic matter (DOM) to metal (oxy)hydroxide mineral surfaces is a critical step for C sequestration in soils. Although equilibrium studies have described some of the factors controlling this process, the molecular-scale description of the adsorption process has been more limited. Chemical force spectroscopy revealed differing adhesion strengths of DOM extracted from three soils and a reference peat soil material to an iron (oxy)hydroxide mineral surface. The DOM was characterized using ultrahigh-resolution negative ion mode electrospray ionization Fourier Transform ion cyclotron resonance mass spectrometry. The results indicate that carboxyl-rich aromatic and N-containing aliphatic molecules of DOM are correlated with high adhesion forces. Increasing molecular mass was shown to decrease the adhesion force between the mineral surface and the DOM. Kendrick mass defect analysis suggests that mechanisms involving two carboxyl groups result in the most stable bond to the mineral surface. We conceptualize these results using a layer-by-layer "onion" model of organic matter stabilization on soil mineral surfaces.

Molecular composition and biodegradability of soil organic matter: a case study comparing two new England forest types.

Soil organic matter (SOM) is involved in many important soil processes such as carbon sequestration and the solubility of plant nutrients and metals. Ultrahigh resolution mass spectrometry was used to determine the influence of forest vegetation type and soil depth on the molecular composition of the water-extractable organic matter (WEOM) fraction. Contrasting the upper 0-5 cm with the 25-50 cm B horizon depth increment, the relative abundance of lipids and carbohydrates significantly increased, whereas condensed aromatics and tannins significantly decreased for the deciduous stand WEOM. No significant abundance changes were found for the coniferous stand DOM. Kendrick mass defect analysis showed that the WEOM of the 25-50 cm B horizon was depleted in oxygen-rich and higher mass components as compared to the 0-5 cm B horizon WEOM, suggesting that higher mass WEOM components with oxygen-containing functionality show greater reactivity in abiotic and/or biotic reactions. Furthermore, using an inoculated 14-day laboratory incubation study and multivariate ordination methods, we identified the WEOM components with H:C > 1.2 and O:C > 0.5 as being correlated most strongly with biodegradability. Our findings highlight the importance of understanding soil depth differences for various forest types in the chemical composition of SOM and the processes governing SOM production and transformations to fully understand the ecological implications of changes in forest composition and function in a changing climate.

Influence of heteroatom pre-selection on the molecular formula assignment of soil organic matter components determined by ultrahigh resolution mass spectrometry.

Soil organic matter (SOM) is involved in many important ecosystem processes. Ultrahigh resolution mass spectrometry has become a powerful technique in the chemical characterization of SOM, allowing assignment of elemental formulae for thousands of peaks resolved in a typical mass spectrum. We investigated how the addition of N, S, and P heteroatoms in the formula calculation stage of the mass spectra processing workflow affected the formula assignments of mass spectra peaks. Dissolved organic matter extracted from plant biomass and soil as well as the soil humic acid fraction was studied. We show that the addition of S and P into the molecular formula calculation increased peak assignments on average by 17.3 % and 10.7 %, respectively, over the assignments based on the CHON elements frequently reported by SOM researchers using ultrahigh resolution mass spectrometry. The organic matter chemical characteristics as represented by van Krevelen diagrams were appreciably affected by differences in the heteroatom pre-selection for the three organic matter samples investigated, especially so for the wheat-derived dissolved organic matter. These results show that inclusion of both S and P heteroatoms into the formula calculation step, which is not routinely done, is important to obtain a more chemically complete interpretation of the ultrahigh resolution mass spectra of SOM.

Emerging investigator series: microplastic-based leachate formation under UV irradiation: the extent, characteristics, and mechanisms.

Microplastics in the aquatic system are among the many inevitable consequences of plastic pollution, which has cascading environmental and public health impacts. Our study aimed at analyzing surface interactions and leachate production of six microplastics under ultraviolet (UV) irradiation. Leachate production was analyzed for the dissolved organic content (DOC), UV254, and fluorescence through excitation emission (EEM) to determine the kinetics and mechanisms involved in the release of organic matter by UV irradiation. The results suggested there was a clear trend of organic matter being released from the surface of the six microplastics caused by UV irradiation based on DOC, UV254 absorbance, and EEM intensity increasing with time. Polystyrene had the greatest and fastest increase in DOC concentrations, followed by the resin coated polystyrene. Experiments conducted at different temperatures indicated the endothermic nature of these leaching mechanisms. The differences in leachate formation for different polymers were attributed to their chemical makeup and their potency to interact with UV. The aged microplastic samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), to determine the surface changes with respect to leachate formation. Results indicated that all microplastics had increasing carbonyl indices when aged by UV with polystyrene being the greatest. These findings affirm that the leachate formation is an interfacial interaction and could be a significant source of organic compound influx to natural waters due to the extremely abundant occurrence of microplastics and their large surface areas.

Fourier transform infrared and fluorescence spectral features of organic matter in conventional and organic dairy manure.

Organic dairy production has exhibited potential for growth in the United States dairy sector. However, little information is available on whether there is any difference in manure composition and quality between organic (OD) and conventional (CD) dairy manure even though the composition and quality are important parameters with respect to availability, utilization, and cycling of manure nutrients and environmental impact evaluation. We comparatively characterized whole and water-extracted materials of 15 OD and seven CD dairy manure samples by Fourier transform infrared (FT-IR) and fluorescence spectroscopies. Fourier transform infrared features of manure organic matter varied mainly in the 1650 to 1550 cm range, reflecting the presence of different N compounds in these manure samples. Fluorescence data revealed five fluorophore components present in the water-extracted organic matter from the manures. We found no clearly distinct value ranges in whole and water-extractable organic matter between the two types of dairy manure with respect to C and N contents and FT-IR and fluorescence spectral features. However, based on the average values, we observed general pattern differences on the effect of organic farming on the manure composition: OD contained less soluble C and N compounds on dry weight basis but more hydrophobic aliphatic groups in whole manure. The soluble organic matter in OD samples contained more stable humic- and lignin-related components and less amino/protein N-related components based on their spectroscopic features. These differences might be attributed to more forage feedstuffs in organic dairy farming management and more protein additives in conventional dairy feedstuffs. Information from this work may be useful in aiding organic dairy farmers in making manure management decisions.

Ultrahigh resolution mass spectrometry and indicator species analysis to identify marker components of soil- and plant biomass- derived organic matter fractions.

The chemical properties of organic matter affect important soil processes such as speciation, solubilization, and transport of plant nutrients and metals. This work uses ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to determine the molecular composition of three organic matter fractions of soils and aqueous extracts of crop biomass. Comparison of the van Krevelen plots allowed tracking the changes in organic matter with increasing humification. Aqueous plant biomass extracts contain a diverse mixture of lipids, proteins, and lignins. Soil aqueous extracts were marked by increases in lignin and carbohydrate components and decrease in the protein component as compared to the plant extract. Refractory humic acid fractions were marked by decrease in the lignin component and increases in the lipid and condensed aromatic components. The multivariate indicator species analysis was used to identify marker components of the four organic matter types investigated. The plant extract group had 772 marker components compared to 237 for soil aqueous extract, 92 for mobile humic acid, and 418 for calcium humic acid. This study demonstrates that ultrahigh resolution mass spectrometry and multivariate methods can be used to identify marker components to gain a molecular-scale description and understanding of C dynamics.

Rapid determination of carbamate pesticides in food using dual counter-current chromatography directly interfaced with mass spectrometry.

Dual counter-current chromatography (dual CCC)-tandem mass spectrometry (MS/MS) was successfully performed with a newly designed spiral column for dual CCC. The small column capacity required for directly coupling with electrospray MS/MS was accomplished by forming a rectangular spiral groove on a plastic disk and sealing it with a PTFE sheet. This novel dual CCC-MS/MS technique was successfully applied for the rapid determination of methomyl, fenobucarb and carbaryl pesticides in food. A two-phase solvent system of n-hexane-acetonitrile-0.1% formic acid (45:45:10) was suitable for both good dual CCC separation and sufficient ionization of pesticides. Recoveries of these three pesticides from mandarin orange and spinach samples fortified at 0.05 mg/kg were in the range of 93-107% with relative standard deviations of 2.4-3.8%.

PowerSlicing to determine fluorescence lifetimes of water-soluble organic matter derived from soils, plant biomass, and animal manures.

Time-resolved fluorescence spectroscopy was used to characterize water-soluble organic matter (WSOM) which plays an important role in soil ecosystem processes. WSOM was extracted from plant biomass, animal manures, and soils from controlled cropping systems studies with known histories of organic amendments. Lifetime constants were derived using the multi-way PowerSlicing method which provides a non-iterative, multi-exponential fitting of decay profiles. The lifetimes obtained by PowerSlicing were not significantly different from those obtained using the traditional discrete components analysis. The three components attributed to WSOM had lifetimes of 0.38 +/- 0.14, 2.11 +/- 0.72, and 7.08 +/- 1.18 ns which are in agreement with previous lifetimes reported for humic substances. This study provides further support for the new paradigm for the structure of soil organic matter where the organic matter is composed of low-molecular-weight components held together by hydrogen bonding and hydrophobic interactions.

Predictive factors for survival for out-born infants born between 23 and 24 weeks of gestation in the post-surfactant era: fourteen years' experience in a single neonatal care unit, 1987-2000.

BACKGROUND: The purpose of the present paper was to identify the predictive factors for survival for out-born infants born between 23 and 24 weeks of gestation. METHODS: Ninety-two infants born between 23 and 24 weeks' gestation who were admitted to a level III neonatal intensive care unit from 1987 to 2000, were retrospectively studied. Survival was defined as discharge from the neonatal intensive care unit. Logistic regression was done to determine which clinical factors were most predictive of survival. The independent variables that were entered into the models were determined by preliminary univariate analysis. RESULTS: Ninety-two infants were enrolled in the present study, 49 of whom survived in the surfactant era. The four variables that were found to be most predictive for survival on logistic regression were systolic blood pressure at 6 h (odds ratio [OR], 1.3; 95% confidence interval [CI]: 1.11-1.44 1 mmHg), ventilatory index < 0.047 (OR, 4.8; 95%CI: 1.07-21.65), initial hemoglobin value (OR, 1.6; 95%CI: 1.09-2.34/1 g/dL), and base excess at 6 h (OR, 2.1; 95%CI: 1.08-1.84/5 mEq/L). CONCLUSIONS: A total of 53.2% of infants delivered between 23 and 24 weeks of gestation survived at discharge after introduction of surfactant replacement therapy. Early cardiopulmonary adaptation and initial hemoglobin value are key factors for survival in infants born at 23-24 weeks of gestation.

Relationship between serum lactate level and periventricular leukomalacia.

In a case control study, we evaluated the serum lactate levels during the early days of life in preterm infants with periventricular leukomalacia (PVL), who were presumed to have suffered injury around birth. Thirteen infants diagnosed by ultrasonography as suffering from cystic PVL during the neonatal period and 26 normally developed infants matched by gestational age were enrolled in the study. The serum lactate level was measured repeatedly during the 72 h after birth. The mean serum lactate levels on admission were 2.95+/-0.43 and 3.21+/-0.29 mmol/L in the PVL and control groups, respectively. There was no statistically significant difference in the serum lactate level between the groups at any point during the first 72 h after birth. In conclusion, the serum lactate level was not elevated in preterm infants with PVL suggesting that the serum lactate level is not a useful predictor for the development of PVL in infants.

Characterization of fresh and decomposed dissolved organic matter using excitation-emission matrix fluorescence spectroscopy and multiway analysis.

Fresh and decomposed dissolved organic matter (DOM) derived from 13 plant biomass and animal manure sources was characterized using multidimensional fluorescence spectroscopy with parallel factor analysis (PARAFAC), high-performance size-exclusion chromatography, and UV-vis spectroscopy. The PARAFAC analysis modeled seven fluorescence components: tryptophan-like, tyrosine-like, and five humic substance-like components. For most of the plant-derived DOM solutions, decomposition significantly affected the concentration of three humic substance-like-associated components, increasing two and decreasing one. The effect of decomposition upon DOM derived from animal manures was dependent on the manure source. For a majority of the DOM extracts, the ratio of fluorescence intensity to absorptivity at 254 nm increased following decomposition, indicating that fluorescing DOM compounds were generally more resistant to biodegradation than nonfluorescing UV-absorbing compounds. Molar absorptivity, humification index (HIX), and apparent molecular weight (MWAP) increased by 38.0, 38.8, and 370%, respectively, following decomposition. Spearman correlation analysis showed a strong positive relationship between the humic substance-like components and the DOM MWAP, absorptivity, and HIX. The results of this study support the use of multidimensional fluorescence spectroscopy with PARAFAC as a method to monitor the decomposition of carbon-rich soil amendments such as crop residues, green manures, and animal manures.