Two-stage wood decay by Grifola frondosa

Abstract

In nature, only white-rot fungi can completely decompose wood biomass in the environmental carbon cycle. However, their degradation strategy is still unclear. Despite many studies on the lab-scale wood-decay process, investigations on the open-field process have been limited by their difficulty. Here, we aimed to elucidate the degradation strategy of white-rot fungi in nature by monitoring the chemical composition changes of logs exposed to the white-rot fungus, Grifola frondosa, over 4 y of cultivation using Fourier transform infrared spectroscopy. Grifola frondosa began to decompose lignin and deacetylate hemicellulose in the first 2 y and then degraded polysaccharides in the next 1 y. Finally, lignin decomposition recurred after the third year. Thus, our study revealed that G. frondosa decayed wood in a repetitive two-stage process: lignin and polysaccharide degradation. The switching cycle may promote efficient degradation.

Keywords: Fourier transform infrared spectroscopy; deacetylation; delignification; white-rot fungi; wood-log cultivation.

Fig. 1 - Experimental design and sampling protocol.

Fig. 2 - Fourier transform infrared spectra of the Quercus serrata logs at various degrees of decay by Grifola frondosa. A: heartwood and B: sapwood. These spectra are typical examples from one of the four replicate samples.

Fig. 3 - Ratios of the height of the lignin-associated peak with polysaccharide peaks for decayed samples. A, C, E: heartwood samples and B, D, F: sapwood samples. These ratios are the ratios of aromatic skeletal in lignin to C-H deformation in cellulose and hemicellulose (A, B), to C-O-C vibration in cellulose and hemicellulose (C, D), and to C-H deformation in cellulose (E, F). p-value: ^* < 0.05 and ^** < 0.01. Significance was analyzed by performing the non-parametric Kruskal-Wallis test combined with Dunn's multiple comparison test.

Fig. 4 - Ratios of the height of the acetyl group of hemicellulose-associated peak with polysaccharide peaks for decayed samples. A, C: heartwood samples and B, D: sapwood samples. These ratios are the ratios of unconjugated C=O in xylans to C-H deformation in cellulose and hemicellulose (A, B) and to C-O-C vibration in cellulose and hemicellulose (C, D). p-value: ^* < 0.05 and ^** < 0.01. Significance was analyzed by performing the non-parametric Kruskal-Wallis test combined with Dunn's multiple comparison test.