Rainfall Promote Bruceine D Release from Brucea javanica Leaf Litter Thus Reducing Weeds and Enhancing Plant Competitiveness.

Brucea javanica (L.) Merr. is a medicinal plant widely cultivated in tropical and subtropical regions, and under the B. javanica plantations region few weed species have been established. This study demonstrated that mulching with moistened B. javanica leaf powder inhibited the emergence of Bidens pilosa and Digitaria sanguinalis seedlings compared to the control, with the inhibitory effect being thickness-dependent. Among the four extracts (methanolic, M; petroleum ether, PE; ethyl acetate, EA; and n-butanol, n-B) of B. javanica leaf powder, both n-B and EA extracts showed significant inhibitory activity in laboratory and greenhouse experiments, which were correlated with their relatively high Bruceine D (BD) content. Further column leaching simulated rainfall demonstrated that decreased rainfall intensity could enhance the herbicidal activity of the B. javanica leaf powder against weed seedling emergence, which significantly coincided with the increased content of BD leached. Our results concluded that BD, may as the main phytotoxic compound in B. javanica leaf litter, could be leached into the soil by rainfall and interfere with the germination and growth of neighboring plants to help B. javanica gain an advantage in the particular habitat.