Organic matter transformations during the weathering process of spent mushroom substrate

The weathering process of spent mushroom substrate (SMS) was studied to better understand the chemical properties and transformations of organic matter (OM) during the process. The SMS was piled (20 m by 6 m row of 1.5 m height) in an open field and weathered during 15 mo. Chemical properties of the OM collected from the top and bottom parts of the weathering pile were studied using ¹³C-nuclear magnetic resonance (NMR), tetramethylammonium hydroxide (TMAH) thermochemolysis-gas chromatograph/mass spectrometry (GC/MS), and pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS). The ¹³C-NMR data suggested that weathered SMS from the top part of the pile degraded rapidly: the relative level of polysaccharides decreased by 33% while the level of aromatic C increased by 21% during the process. The TMAH thermochemolysis chromatogram exhibited peaks of methylated derivatives of phenyl, guaiacyl and syringyl structures as well as some fatty acid methyl esters. Lignin-derived products from TMAH thermochemolysis indicate that preferential degradation of syringyl units and oxidation of Cα-Cβ bonds occurred in the SMS from the top part of the pile. In contrast, no major changes in lignin-derived structures were observed in the weathered SMS from the bottom part of the pile. The ¹³C-NMR, Py-GC/MS and TMAH thermochemolysis-GC/MS analyses indicated that the SMS decomposed rapidly at the top part of the weathering pile, whereas decomposition at the bottom of the pile was significantly slower, probably due to lack of oxygen. These analyses were shown to be useful techniques for the characterization of degradation processes in SMS. Therefore, their application to studies on OM transformation and humification processes is highly recommended.