Autotoxic effects of root exudates of soybean

To examine whether the autotoxicity due to root exudates was involved in the growth reduction in soybean monocropping, soybean seedlings were grown in a newly prepared nutrient solution or those after one or two soybean cropping with or without the addition of activated charcoal. Monocropping of soybean decreased both plant biomass and root TTC reducing activity. These decreases, however, were significantly alleviated by the addition of activated charcoal. Meanwhile root exudates from reproductive growth stage, showed higher autotoxicity than those from vegetative growth stage. Moreover, seedlings after exposure to root exudates exhibited higher activity of superoxide dismutase (SOD) and guaiacol peroxidase (POD). All these suggest that soybean root exudates have autotoxic potential and are actively involved in the soil sickness in soybean production.