Biochar (BC) is a carbon rich product resulting from the biomass pyrolysis process and there have been no reports until now on BC effects in tissue cultures as a suitable substitute for activated charcoal (AC). The results of an experiment on two clones of white poplar (Populus alba L.) grown in culture media with different amounts of BC (0, 0.5 and 1.5 g/dm3) showed that its addition did not damage the plants and there were no significant differences comparing the data obtained for the same concentrations of AC. Both BC and AC addition was shown to increase root dry biomass and number of roots per shoot and these effects appeared to be independent of genotype and concentrations of the added products. A greater elongation was also recorded for shoots grown on a substrate containing BC than those grown on media without BC. These effects did not seem to be caused by darkening due to the addition of BC as there are no significant differences between the temperatures of the different culture media, but are probably due to the adsorption of molecules such as ethylene. Indeed, during the experiment, the hormone concentration in the atmosphere was lower in vials containing the media with BC than the BC-free ones after 14 and 21 days: the lower amount of ethylene in the medium with BC could explain the difference in shoot elongation and the abundant root biomass since high ethylene concentration could inhibit organogenesis.
