Abstract:

The invasive alien plant Ipomoea cairica is widespread throughout South China. Allelopathy has been considered a key mechanism to explain the invasiveness of this species. In this research， bioassays showed that the germination of Bidens pilosa and Lactuca sativa seeds was significantly inhibited when mimicking the natural volatile and leaching conditions that would occur near plants of I. cairica. Substances released in these two ways were collected and analyzed by gas chromatography and mass spectrometry （GC-MS）. The volatiles from I. cairica contained 18 terpenes， of which caryophyllene （28.17%）， β-ocimene （16.59%）， α-pinene （13.65%）， and （+）-β-cedrene （9.43%） had the highest relative contents. The rain leachates were mainly phenolic acids， with the four with highest relative contents being cinnamic acid （39.21%）， succinic acid （15.15%）， propionic acid （11.12%） and lauric acid （9.38%）. Further analyses of these eight main chemicals were conducted to determine their actual concentrations in collected vapors and leachates. At these actual concentrations， laboratory bioassay results showed that cinnamic acid and lauric acids significantly inhibited the seed germination of B. pilosa and L. sativa seeds. In contrast， propionic acid and succinic acid didn’t show a significant adverse effect. Similarly， for the main volatiles present， the germination of B. pilosa and L. sativa seeds was significantly inhibited by treatment with （+）-β-cedrene and caryophyllene， while there was no noticeable effect when the seeds were treated with α-pinene or β-ocimene. In summary， some terpenes and phenolic acids were phytotoxic to other plant species when they were released as volatiles or by rain leaching from I. cairica.

Key words: allelopathic effects, Ipomoea cairica, volatile, rain leaching, terpenes, phenolic acids