Abstract: A bioassay was conducted to examine the allelopathic activities of five reported allelopathic substances in barnyard grass,i.e., 2,4-bis (1,1-dimethylethyl) phenol, p-hydroxymandelic acid, and three kinds of phthalate esters, on rice, barnyard grass, and lettuce. HPLC was used to analyze the contents of the five compounds and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in barnyard grass tissues, root exudates, and rhizosphere soil.At concentration 100 μg·^-1, 2,4-bis (1,1-dimethylethyl) phenol had the strongest inhibitory effect on rice, lettuce and barnyard grass, while p-hydroxymandelic acid had the weakest one. Dimethyl-ester-phthalic acid, diisooctyl ester-phthalic acid, and 2,4-bis (1,1-dimethylethyl) phenol exhibited greater inhibition on barnyard grass than on rice. HPLC analysis showed that the p-hydroxymandelic acid concentration in barnyard grass shoots, roots, and root exudates at seedling stage was 9.72 μg·g^-1, 7.29 μg·g^-1, and 0.24 μg·ml^-1, respectively.No p-hydroxymandelic acid was detected at other growth stages of barnyard grass and its rhizosphere soil. 2,4-bis (1,1-dimethylethyl) phenol, DIMBOA, and phthalate esters were not detected in all samples. The dose-response trial on p-hydroxymandelic acid showed no significant effect on target plants. It was concluded that p-hydroxymandelic acid was not the main allelochemicals in barnyard grass, and the reported 2,4-bis (1,1-dimethylethyl) phenol, DIMBOA, and three phthalate esters were not detected in barnyard grass.

Key words: Castanea henryi, Nutrient element, System analysis, Simulation