Title: Spatial arrangement of organic compounds on model mineral surface: Implications for soil organic matter stabilization.

The complexity of the mineral organic carbon interface may influence the extent of stabilization of organic carbon compounds in soils, which is important for global climate futures. The nanoscale structure of a model interface was examined here by depositing films of organic carbon compounds of contrasting chemical character, hydrophilic glucose and amphiphilic stearic acid, onto a soil mineral analogue (Al2O3). Neutron reflectometry, a technique which provides depth-sensitive insight into the organization of the thin films, indicates that glucose molecules reside in a layer between Al2O3 and stearic acid, a result that was verified by water contact angle measurements. Molecular dynamicsmore » simulations reveal the thermodynamic driving force behind glucose partitioning on the mineral interface: The entropic penalty of confining the less mobile glucose on the mineral surface is lower than for stearic acid. The fundamental information obtained here helps rationalize how complex arrangements of organic carbon on soil mineral surfaces may arise« less

This study investigates the spatial distribution of organic carbon (C) in free stable microaggregates (20-250 {mu}m; not encapsulated within macroaggregates) from one Inceptisol and two Oxisols in relation to current theories of the mechanisms of their formation. Two-dimensional micro- and nano-scale observations using synchrotron-based Fourier-transform infrared (FTIR) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy yielded maps of the distribution of C amounts and chemical forms. Carbon deposits were unevenly distributed within microaggregates and did not show any discernable gradients between interior and exterior of aggregates. Rather, C deposits appeared to be patchy within the microaggregates. In contrast to themore » random location of C, there were micron-scale patterns in the spatial distribution of aliphatic C-H (2922 cm-1), aromatic C=C and N-H (1589 cm-1) and polysaccharide C-O (1035 cm-1). Aliphatic C forms and the ratio of aliphatic C/aromatic C were positively correlated (r 2 of 0.66-0.75 and 0.27-0.59, respectively) to the amount of O-H on kaolinite surfaces (3695 cm-1), pointing at a strong role for organo-mineral interactions in C stabilization within microaggregates and at a possible role for molecules containing aliphatic C-H groups in such interactions. This empirical relationship was supported by nanometer-scale observations using NEXAFS which showed that the organic matter in coatings on mineral surfaces had more aliphatic and carboxylic C with spectral characteristics resembling microbial metabolites than the organic matter of the entire microaggregate. Our observations thus support models of C stabilization in which the initially dominant process is adsorption of organics on mineral surfaces rather than occlusion of organic debris by adhering clay particles.« less

No abstract prepared.

Coal is a complex, heterogeneous solid that includes interdispersed mineral matter. However, knowledge of organic-mineral matter interactions is embryonic, and the impact of these interactions on coal pyrolysis and liquefaction is incomplete. Clay minerals, for example, are known to be effective catalysts for organic reactions. Furthermore, clays such as montmorillonite have been proposed to be key catalysts in the thermal alteration of lignin into vitrinite during the coalification process. Recent studies by Hatcher and coworkers on the evolution of coalified woods using microscopy and NMR have led them to propose selective, acid-catalyzed, solid state reaction chemistry to account for retainedmore » structural integrity in the wood. However, the chemical feasibility of such reactions in relevant solids is difficult to demonstrate. We have begun a model compound study to gain a better molecular level understanding of the effects in the solid state of organic-mineral matter interactions relevant to both coal formation and processing. To satisfy the need for model compounds that remain nonvolatile solids at temperatures ranging to 450{degrees}C, model compounds are employed that are chemically bound to the surface of a fumed silica (Si-O-C{sub aryl} linkage). The organic structures currently under investigation are phenethyl phenyl ether (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}OC{sub 6}H{sub 5}) derivatives, which serve as models for {Beta}-alkyl aryl ether units that are present in lignin and lignitic coals. The solid-state chemistry of these materials at 200-450{degrees}C in the presence of interdispersed acid catalysts such as small particle size silica-aluminas and montmorillonite clay will be reported. Our initial focus will be on defining the potential impact of these interactions on coal pyrolysis and liquefaction.« less

Barley (Hordeum vulgare L. cultivar Atlas 57) was grown in desert soil from bare areas (low soil organic matter) and in soil from beneath long established shrubs (moderately high soil organic matter). The plants were grown in pots with three replicates and with and without N fertilizer. Nitrogen fertilizer overcame only part of the yield decrease resulting from the low organic matter soil in that plants grown in soil from under shrubs produced three times as much dry weight as the low organic matter soil with N added. Plants in the high organic soil also responded to N. Silicon levelsmore » in barley were decreased by N fertilizer and were higher in the plants from the low organic matter soil with and without N. Iron, Al, and Zn concentrations in the shoots were positively correlated with N concentrations and negatively with those of Si. The plants grown in the low organic matter soil were high in Mn. Calcium was positively correlated with Ba concentrations in shoots. Calcium and Mg were negatively correlated with each other as were Sr and Ba.« less