Fig. 2. The relative proportions of C in six functional regions, expressed in grams of C per 100 grams of total organic C (TOC), in the original soil (black), and in the <53-µm fractions (hatched) after photo-oxidation as determined by solid-state ¹³C cross-polarization magic-angle spin nuclear magnectic resonance (CPMAS NMR) spectroscopy.