Chemical Characterization of Sclerotia Grains Collected from a Volcanic Ash Soil Profile in Japan

Abstract

Sclerotia grains, fungal resting structures, are commonly found in forest soils, but little is known of their chemical characteristics. Sclerotia samples collected from a buried A horizon from a Japanese Andosol were physically and chemically characterized by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), Fourier-transform infrared spectrometry, elemental (C-H-N-O) analysis, ¹³C nuclear magnetic resonance, ²⁷Al nuclear magnetic resonance, particle induced X-ray emission spectrometry, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. The C, H, N, and O contents of the sclerotia grains were determined to be 47.6, 3.32, 0.78, and 30.2% by mass, respectively. Sclerotia Al, Fe, and Si contents determined by particle induced X-ray emission analysis were 1.4, 0.56, and 0.08%, respectively, in relative agreement with those determined by inductively coupled plasma optical emission spectrometry (1.1, 0.5, and 0.1%, respectively). Functional carbon groups were characterized by dominance of O-alkyl carbon associated with aromatic carbon. Analysis of the ²⁷Al nuclear magnetic resonance spectra showed the presence of 6- and 4-coordinated aluminum. X-ray diffraction analysis showed that the dominant form of aluminum in sclerotia was amorphous. Minor elements such as Ti, Cr, Mn, Cu, Zn, Br, and Pb were detected in the grains at concentrations between 10 and 100 μg g⁻¹.