Response in vitro of lignin degrading fungi to single or combined applications of a biochar and a compost humic acid

The fungi Stereum hirsutum, Irpex lacteus, Phanerochaete chrysosporium, Bjerkandera adusta, Trametes versicolor and Pleurotus ostreatus were treated in vitro with a biochar (BC) from red spruce wood at doses of 0.2% (w/v, BCLD) and 1% (BCHD), the BC water extract (BCWE) at doses of 0.2% (w/v, BCWELD) and 1% (BCWEHD), a compost humic acid (HA) at a concentration of 200 mg L-1and combinations BCWE-HA. All BC treatments stimulated P. ostreatus growth (up to 26%). T. versicolor growth was increased (up to 10%) and reduced (down to 33%) by BCLDand BCHD, respectively. All the other fungi were always inhibited by BC (down to 59% for B. adusta with BCHD). BCWELDincreased hyphal elongation of B. adusta and T. versicolor up to 22% and 12%, respectively, whereas BCWEHDslightly reduced that of B. adusta. In general, both HA alone and all combinations BCWE-HA at both doses significantly stimulated mycelial growth of B. adusta, T. versicolor and P. ostreatus (up to 22% for B. adusta) or were irrelevant. These findings indicate that when BC is incorporated in soil, BC activity in vitro on ligninolytic fungi might be considerably modified by the contents of water and humic substances present in soil.