The contribution of volatilization and exudation to the allelopathic phytotoxicity of invasive Chrysanthemoides monilifera subsp. monilifera (boneseed).
Negative plant-plant interactions through the release of allelochemicals via leaching, decomposition of residues in soil, volatilization and exudation are well established. We aimed to characterise the allelopathic potential of Chrysanthemoides monilifera subsp. monilifera (boneseed) in terms of volatilization and exudation. A series of bioassays compared dose-response to volatilization impacts of boneseed organs on model species Lactuca sativa and associated native Acacia mearnsii with particular reference to investigating physiological and biochemical interference through excessive reactive oxygen species (ROS) production. The impact of boneseed exudates on native Xerochrysum bracteatum and A. mearnsii were investigated in greenhouse. We found significant dose-response impacts of boneseed volatilization in the order of root>leaf>stem on biometric parameters of both of the test species with more significant impact on L. sativa while impact on germination indices was negligible. Hydrogen peroxide, lipid peroxidation and electrolyte leakage in the test species seedlings was increased with increasing doses of boneseed organs, suggesting cellular fragmentation, and a potential mechanism of allelopathic impact through excessive ROS production. Boneseed exudates killed X. bracteatum and inhibited growth parameters of A. mearnsii significantly which was partially reduced by activated carbon treatments. The increase of free proline in A. mearnsii and phenolics in soil, and decrease of soil dehydrogenase activities indicated that boneseed led to a stressed condition in the neighboring species. Our findings help to explain the mechanism of invasion by boneseed and emphasize the importance of mitigating the effects of allelopathy by boneseed to protect native and crop species.