Ambrosia artemisiifolia and Ambrosia trifida are annual invasive plants that cause serious harm to agriculture, animal husbandry, and human health. Based on the important characteristic of high-density, cluster distribution of their populations, it is speculated that its autotoxins have an effect on density regulation. This study explored the regulation of autotoxicity on intraspecific density. We used water extracts from two plants to compare and verify the autotoxicity of seed germination, analysed the components of autotoxins. The results showed that A. artemisiifolia and A. trifida had significant autotoxicity, and the highest inhibition rates on seed germination were 27.21% and 77.94%, respectively; ultra-performance liquid chromatography tandem mass spectrometry analysis revealed that chlorogenic acid, caffeic acid, p-coumaric acid, and vanillin were the main autotoxins of the two plants. After the seeds were washed with water, the germination recovery rate of seeds increased with the increased of inhibition degree of autotoxins treatment. Therefore, this study verified the autotoxicity of A. artemisiifolia and A. trifida, which can promote and inhibit the seed germination of A. artemisiifolia and A. trifida to regulate intraspecific competition.

Common ragweed (Ambrosia artemisiifolia) is an invasive annual weed that invades heavily disturbed habitats and natural habitats less disturbed by human activities with native plant species in need of protection. Achieving effective control of A. artemisiifolia for the protection of native organisms and the local ecological environment is an ongoing challenge. Based on the growth and development characteristics of A. artemisiifolia, we examined the effectiveness of herbicides in controlling this species and the optimal time for application in the field with the aim of reducing herbicide dosage. Additionally, we analyzed whether the efficiency of low-dose applications for controlling this species might improve with increasing native plant species richness. Our findings indicate that aminopyralid (33 g ai ha−1) was the most suitable herbicide for chemical control of A. artemisiifolia, with optimum application time being during vegetative growth (BBCH 32–35). Application of aminopyralid was found to kill approximately 52% of A. artemisiifolia plants, and more than 75% of the surviving plants did not bloom, thereby reducing seed yield of the population by more than 90%. Compared with the application of high-dose herbicide, the phytotoxicity of aminopyralid to native plants at the applied dose was substantially reduced. After 2 years of application, the relative coverage of A. artemisiifolia significantly decreased, with few plants remaining, whereas the relative coverage of native plants more than doubled, representing an eco-friendly control. Further, there was an increase in the A. artemisiifolia control rate in the plant community with higher native plant species richness at the same herbicide rates and a reduction in seed yield of A. artemisiifolia. Our findings help toward developing control measures to reduce the invasiveness of A. artemisiifolia with low-dose herbicides meanwhile protecting native plants, and then using the species richness of native plant communities to indirectly promote the effectiveness of low-dose herbicide application.

Rapid monitoring and early elimination are important measures to control the spread of invasive plants. Ambrosia artemisiifolia is a globally distributed harmful invasive weed. The aim of this study was to clarify the invasion habitat preferences of A. artemisiifolia and the interspecific associations or phylogenetic relationships between this and native species in the Yili River Valley of Xinjiang, China. We identified the preferred habitat types of A. artemisiifolia, and investigated the composition and distribution of native species at the early stage of invasion by targeted sampling at 186 sites. By comparing the associations and phylogenetic distance between A. artemisiifolia and native species with those in Xinjiang and worldwide, we assessed the feasibility of using native species as indicators for rapid monitoring of A. artemisiifolia. A. artemisiifolia displayed an obvious invasive preference for semi-arid areas, particularly road margins (27.96%), forest (21.51%), farmland (19.35%), wasteland (12.37%), residential areas (10.75%), and grassland (8.06%). The composition and distribution of native species were similar across habitats, with more than 50% co-occurrence of A. artemisiifolia with Setaria viridis, Poa annua, Arrhenatherum elatius, Artemisia annua, Artemisia vulgaris, Artemisia leucophylla, Cannabis sativa, and Chenopodium album. A. artemisiifolia was more likely to show co-occurrence with closely related species. Overall, 53.85% of the above indicator native species with high co-occurrence were widely distributed in the potential suitable areas for A. artemisiifolia in Xinjiang. Globally, the species with the highest occurrence belonged to the genera Chenopodium (58%), Bromus, Poa, Setaria, and Trifolium (>40%). Therefore, native species with the strong association and phylogenetic distant relationship to A. artemisiifolia can be employed as indicators for rapid and accurate monitoring in semi-arid areas.