Investigating the effects of biochar colloids and nanoparticles on cucumber early seedlings

Understanding about the influence of biochar colloidal and nanoscale particles on plant is limited. We therefore extracted the colloids and nanoparticles from hot pepper stalk biochar (CB600 and NB600), and examined physiological responses of cucumber early seedlings through hydroponic culture and pot experiment. CB600 had no significant effect on shoot at 500 mg/L, while it decreased root biomass and inhibited lateral root development. The biomass and root length, area, and tip number dramatically reduced after 500 mg/L NB600 treatment. Water content of NB600-exposed shoot was lower, suggesting water uptake and transfer might be hindered. For resisting exposure stress, root hair number and length increased. Even, the study observed swelling and hyperplasia of root hairs after direct exposure of CB600 and NB600. These adverse effects might be associated with the contact and adhesion of CB600 and NB600 with sharp edges to root surface. For a low concentration of 50 mg/L, NB600 did not influence cucumber early seedlings. In soil, CB600 and NB600 did not cause inhibitory effect at relatively high contents of 500 mg/kg and 2000 mg/kg. This study provides useful information for understanding phytotoxicity and environmental risk of biochar colloids and nanoparticles, which has significant implications with regard to biochar application safety.