Microaggregates are recognized as repository of the most stable organic carbon (C) pool in soil. Biochemical recalcitrance, chemical stabilization and physical protection are the three main mechanisms which involve in organic C protection in soil. The objectives of this study were to image C and other relevant elemental distribution in intact soil microaggregates to understand micro-scale associations and interactions of soil C, soil biota and soil minerals within soil aggregates; and relate these observations to SOC chemistry and aggregate mineralogy.

Oxisols which had been under two tillage systems (till and no-till) with complex crop rotation for 28 years were collected from Center of Experimentation and Research FUNDACEP in Cruz Alta – RS, Brazil. Free soil microaggregates (150-250 µm) were isolated, saturated with e-pure water for 18 hours and followed by shock-freezing in liquid nitrogen. Then, 100-nm ultrathin sections were obtained using a cryo-ultramicrotome.  This procedure allows the spatial arrangement within soil aggregate to be preserved.

NEXAFS-STXM analyses were performed at the Advanced Light Source, Berkeley (beamline 5.3.2) at K- C and N and L-edges of other relevant elements. Results will be presented with the emphasis that how interactions between aggregate architecture, mineralogy and chemistry impact SOC protection in this studied tropical oxisols.