A molecular zoom into soil Humeome by a direct sequential chemical fractionation of soil Marios Drosos ⁎, Antonio Nebbioso, Pierluigi Mazzei, Giovanni Vinci, Riccardo Spaccini, Alessandro Piccolo ⁎ Centro Interdipartimentale di Ricerca sulla Risonanza Magnetica Nucleare per l'Ambiente, l'Agroalimentare ed i Nuovi Materiali (CERMANU), Università di Napoli “Federico II”, via Università 100, 80055 Portici, Italy HIGHLIGHTS • Soil Humeome was for the first time di- rectly fractionated from soil. • 235% more carbon extracted by Humeomics than traditional alkaline extraction. • Separation of soil Humeome unraveled soil organominerals arrangement. • HR-ESI-Orbitrap-MS revealed humic molecules covalently bound to Fe and AlSi. • 66% of unextractable carbon by alkaline solution was solubilised by Humeomics. GRAPHICAL ABSTRACT abstract article info Article history: Received 23 December 2016 Received in revised form 7 February 2017 Accepted 7 February 2017 Available online xxxx Editor: Jay Gan A Humeomics sequential chemical fractionation coupled to advanced analytical identification was applied direct- ly to soil for the first time. Humeomics extracted ~ 235% more soil organic carbon (SOC) than by the total alkaline extraction traditionally employed to solubilise soil humic molecules (soil Humeome). Seven fractions of either hydro- or organo-soluble components and a final unextractable humic residue were separated from soil. These materials enabled an unprecedented structural identification of solubilised heterogeneous humic molecules by combining NMR, GC–MS, and ESI-Orbitrap-MS. Identified molecules and their relative abundance were used to build up structure-based van Krevelen plots to show the specific contribution of each fraction to SOC. The step- wise isolation of mostly hydrophobic and unsaturated molecules of progressive structural complexity suggests that humic suprastructures in soil are arranged in multi-molecular layers. These comprised molecules either hydrophobically adsorbed on soil aluminosilicate surfaces in less stable fractions, or covalently bound in amor- phous organo-iron complexes in more recalcitrant fractions. Moreover, most lipid molecules of the soil Humeome appeared to derive from plant polyesters rather than bacterial metabolism. An advanced understand- ing of soil humic molecular composition by Humeomics may enable control of the bio-organic dynamics and reactivity in soil. © 2017 Elsevier B.V. All rights reserved. Keywords: SOM Humic molecules Humeomics Structural identification Carbon stabilization Organomineral complexes 1. Introduction Soil contains the largest terrestrial pool of organic carbon (OC), with global estimates ranging from 1115 to 2200 Pg (Batjes, 2014). Recent evaluations of SOC dynamics have shown that 20–40% of carbon stored as organic matter (OM) in the upper soil layers has turnover times Science of the Total Environment xxx (2017) xxx–xxx ⁎ Corresponding authors. E-mail addresses: drosos.marios@gmail.com (M. Drosos), antonio.nebbioso@unina.it (A. Nebbioso), pierluigi.mazzei@unina.it (P. Mazzei), giovanni.vinci@unina.it (G. Vinci), riccardo.spaccini@unina.it (R. Spaccini), alessandro.piccolo@unina.it (A. Piccolo). STOTEN-21996; No of Pages 10 http://dx.doi.org/10.1016/j.scitotenv.2017.02.059 0048-9697/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Please cite this article as: Drosos, M., et al., A molecular zoom into soil Humeome by a direct sequential chemical fractionation of soil, Sci Total Environ (2017), http://dx.doi.org/10.1016/j.scitotenv.2017.02.059