Abstract: Autotoxicity of root exudates is a main reason of coffee continuous cropping obstacle, and grafting is considered as an effective way of alleviating autotoxicity. To clarify the autotoxicityinhibition mechanism of grafting, the allelopathy effect of root exudates of cultivated varieties on grafted plants was measured using a pot experiment. The results showed that the growth of ownrooted coffee was inhibited by root exudates, and the inhibition was strengthened with the increased concentration of root exudates. The growth of grafted coffee was promoted by low concentration of root exudates. The plant height, root length, shoot dry weight and root dry weight of grafted coffee were increased by 22.15%, 6.52%, 44.80% and 20.67% respectively. The root activity and leaf protective enzyme activities were significantly increased. The growth of grafted coffee was not improved by high concentration of root exudates, but still the grafted coffee could grow better compared with the ownrooted coffee; the POD activity, CAT activity and SOD activity were increased by 60.61%, 27.27% and 18.24% respectively. The root activity was significantly increased, and MDA content was significantly decreased. In conclusion, under the treatment of root exudates, some factors such as the leaf protective enzyme activities were increased by grafting, and the growth inhibition was reduced or even the growth was promoted.

Key words: Populus alba×P. berolinensis, excretion mechanism., Lymantria dispar, food utilization, heavy metal stress