Characterisation of silver fir wood decay classes using sugar metabolites detected with ion chromatography

Coarse Woody Debris (CWD) is significant both for maintaining biodiversity and global carbon dynamics. As a consequence of global warming, a decrease in CWD could be expected due to enhanced decomposition rates. To describe CWD decay stages, the most widely adopted classification is a five decay-class system developed by Hunter; however, wood chemical characterisation is often lacking. The aims of this work were to study the sugar profiles of living silver fir (Abies alba Mill.) trees and CWD samples in Hunter’s five decay classes, also evaluating the trends and variability in sugar content in CWD samples during decomposition. Ten wood cores from living trees and five replicates of wood samples taken from a single log and from different logs were collected at two mountain sites in northern Italy in two different seasons. Both living trees and CWD samples were analysed using high-performance anion-exchange chromatography, equipped with integrated pulsed amperometric detector and charge aerosol (HPAEC-PAD-CAD) to identify and quantify carbohydrates. Different concentrations of monosaccharides (arabinose, fructose, galactose, glucose, mannose and xylose), disaccharides (cellobiose, maltose sucrose and trehalose), sugar alcohols (myo-inositol and sorbitol) and unknown compounds were detected. Arabinose, maltose, trehalose and unknown compounds showed the same trend during decay stages, while the other sugars showed variations between different sites. Principal Component Analysis (PCA) was performed to assess whether sugar profiles characterised the distribution of the different decay stages. This study is the first attempt to investigate the glucids production during deadwood decomposing process in nature.