Abstract:

As an invasive plant, Bidens pilosa imposes great potential harm to agricultural production, biodiversity and safety of ecosystems. Making use of allelopathy to develop new herbicides, is a meaningful way to control and reduce negative impact of chemical herbicides to the environment. It has been reported that leaf litters of common species, such as Eucalyptus grandis, Cinnamomum camphora and Juglans regia, could generate secondary metabolites during their growing process, which show comparatively strong allelopathy to plants and microorganism, and might play an important role in the prevention of colonial invasion herbs. Selected leaf litters of E. grandis, C.camphora and J.regia,were made into different concentrations of water extracts. By combining the methods of indoor germination test and potted biological test,  indexes such as germination rate, germination speed,  aerial parts fresh weight,  antioxidant enzyme activity, and osmotic regulation substance of B. pilosa were determined. Finally, comprehensive evaluation and comparison of allelopathy effects of the three species were completed. The water extracts of E. grandis leaf litter significantly inhibited the germination rate and germination speed of B. pilosa, while C. camphora and J. regia showed weaker inhibition. The leaf litter water extracts of the three tree species promoted the activity of peroxidase (POD), superoxide dismutase (SOD) and inhibited the activity of catalase (CAT) in B. pilosa. The antioxidant enzyme system of B. pilosa treated withE.grandis leaf litter extract showed passivation response, and thus lead to obvious increase of malondialdehyde (MDA). When treated with leaf litter extracts of E. grandis and C. camphora, the soluble protein and soluble sugar in B. pilosa increased with increasing extract concentration.However, when  treated by leaf litter extracts of J. regia, the soluble protein and soluble sugar in B. pilosa showed a trend of promotion at low concentration, and inhibition at high concentration. Overall, the leaf litter of three tree species showed potential allelopathic effects on the germination and growth of B. pilosa, and led to significant changes in resistance physiological indicators in B. pilosa, but the effects varied by the tree species and the extract concentration of leaf litter. Among them, E.grandisdemonstrated the strongest inhibition on B. pilosa, followed by C.camphora, and J. regiais the weakest.

Key words: allelopathy, leaf litter, Bidens pilosa, invasive plants, resistance physiology