| AVS 66th International Symposium & Exhibition | |
| Applied Surface Science Division | Thursday Sessions |
| Session AS-ThP |
| Session: | Applied Surface Science Poster Session |
| Presenter: | Mark Engelhard, Pacific Northwest National Laboratory |
| Authors: | M.H. Engelhard, Pacific Northwest National Laboratory R. Kukkadapu, Pacific Northwest National Laboratory T. Varga, Pacific Northwest National Laboratory R. Boiteau, Pacific Northwest National Laboratory L. Kovarik, Pacific Northwest National Laboratory J. Cliff, Pacific Northwest National Laboratory M. Wirth, Pacific Northwest National Laboratory A. Dohnalkova, Pacific Northwest National Laboratory C. Smallwood, Pacific Northwest National Laboratory D.E. Perea, Pacific Northwest National Laboratory J. Moran, Pacific Northwest National Laboratory K. Hofmockel, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Warden Soil (alkaline, fine sandy loam) from Prosser, WA was characterized by a suite of spectroscopic and microscopic techniques to gain insights into the nature of mineral-associated soil organic matter (SOM) and its stability under environmental perturbations (e.g., after spiking the soil with siderophores, fluctuating redox conditions, etc.). This approach was undertaken since: a) SOM associated with minerals has been recognized to be relatively stable with respect to biological degradation compared with particulate organic matter (POM), and b) the stability of mineral-OM moieties is primarily a function of interaction between the mineral and OM type, and their physical accessibilities by organisms, oxidants, etc.
Coupled Mössbauer spectroscopy and XRD measurements revealed that ~60-65% of total Fe (5.5 wt.%) in the soil was present in feldspars. The balance of the Fe was primarily partitioned as magnetite, ilmenite, and a suite of nano-Fe(III)-oxides. Various forms of Ca were evident in TEM as: a) “Ca-OM polymers”, b) CaCO3 coated with Ca-OM (consistent with XPS results), and c) Ca feldspar. OM-coated magnetite particles were also evident in TEM results. XPS measurements also demonstrated various types of surface organic C (20-25× that of bulk): a) aliphatic and aromatic C-(C-H), such as C-C, C=C, C-H, b) C-(O,N) bonds as in carbohydrates and amines, c) C displaying bonds to oxygen as in aldehydes, ketones, and amides (C=O, O-C-O, O=C-N), and iv) carboxylic C (O-C=O. NanoSIMS results of 13C- and 15N-labeled siderophore-spiked soils showed that Ca-OM phases rather than Fe-OM phases were preferential hosts for siderophores implying weaker but quickly forming interactions were preferentially established and stable enough to exist in calcareous environments. This provides a potential explanation of the lack of pyoverdines/catechols (siderophores) observed in grassland soils, and more broadly demonstrates the importance of adsorption kinetics rather than thermodynamic equilibrium on the fate and preservation of SOM.