Biochar and hydrochar from waste biomass promote the growth and enzyme activity of soil-resident ligninolytic fungi

Biochar (BC) and hydrochar (HC) are carbonaceous products obtained through, respectively, pyrolysis and hydrothermal carbonization processes of biomass. Both materials are multi-functional soil amendments. Ligninolytic fungi are primary decomposers of recalcitrant lignocellulosic material in nature through their extensive hyphal network and enzymes. In this work, two BC samples from red spruce pellets (BC(SP)) and grapevine pruning residues (BC(GV)) and two HC samples from urban pruning residues (HC(UP)) and the organic fraction of solid urban wastes (HC(SU)) were tested at concentrations of 0.4% and 2% (w/v) on the growth and enzyme activity of Trametes versicolor, Pleurotus ostreatus and Pleurotus eryngii. In all treatments with the lower concentration, BC and HC significantly stimulated fungal growth (up to about 90% increase for HC(SU) on T. versicolor), whereas at the higher dose some inhibition was observed on T. versicolor by BC(SP) and P. ostreatus by BC(SP), BC(GV) and HC(UP). The two materials, especially HC, at both doses noticeably increased the activity of laccase from T. versicolor and P. eryngii, up to 21 and 13 times, respectively, for HC(UP) compared to controls. The activity of manganese peroxidase from P. ostreatus was also greatly stimulated by BC and HC, especially when added at the higher concentration. The overall results obtained in this study suggest potential benefits for ligninolytic fungi from the presence of these materials in soil at adequate dose of application.