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In this paper, we propose a structure for organo-mineral associations in soils based on recent insights concerning the molecular structure of soil organic matter (SOM), and on extensive published evidence from empirical studies of organo-mineral interfaces. Our conceptual model assumes that SOM consists of a heterogeneous mixture of compounds that display a range of amphiphilic or surfactant-like properties, and are capable of self-organization in aqueous solution. An extension of this self-organizational behavior in solution, we suggest that SOM sorbs to mineral surfaces in a discrete zonal sequence. In the contact zone, the formation of particularly strong organo-mineral associations appears to be favored by situations where either (i) polar organic functional groups of amphiphiles interact via ligand exchange with singly coordinated mineral hydroxyls, forming stable inner-sphere complexes, or (ii) proteinaceous materials unfold upon adsorption, thus increasing adhesive strength by adding hydrophobic interactions to electrostatic binding. Entropic considerations dictate that exposed hydrophobic portions of amphiphilic molecules adsorbed directly to mineral surfaces be shielded from the polar aqueous phase through association with hydrophobic moi

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stable isotopes, differential scanning calorimetry (DSC), scanning transmission X-ray microscopy (STXM), near edge x-ray absorption fine structure spectroscopy (NEXAFS) 2 AbstractSoil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. While these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline CuO oxidation to explore this assumption. Specifically, we examined material from the 2.3-2.6 kg L Therefore, our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as co-determined by the interaction between substrates, microbial actors and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or "recalcitrant" compounds will erroneously attribute a greater temperature sensitivity to those materials than they may actually possess.