Identification of anthecotuloide reveals a chemical mechanism underlying Anthemis cotula L. invasiveness

Allelopathy underpins the competitive success of many invasive plants, yet direct chemical ecological links remain scarce. Here, we combined untargeted metabolomics with bioassays to analyse the allelopathic role of the invasive Anthemis cotula, and examine how its signature allelochemical drives invasion dynamics through differential phytotoxic effects on co-occurring plant species.

LC-QTOF metabolite profiling of leaf litter, roots, root exudates, and soils from invaded and uninvaded sites was performed to identify signature metabolites. The sesquiterpene lactone anthecotuloide, characteristic of A. cotula, was structurally confirmed via 1H-NMR and isolated in pure form by targeted HPLC. Bioassays were conducted using four co-occurring plant species- Plantago lanceolata, Plantago major, Sisymbrium orientale, and Trifolium pratense- together with A. cotula itself. Seeds of these plants were exposed to anthecotuloide at the field-relevant concentration (1.06 µg mL-1) and at progressively higher concentrations to establish a dose-response relationship. Seed germination, seedling growth, biomass accumulation, and photosynthetic pigment content were subsequently measured.

Anthecotuloide was exclusive to invaded soils and A. cotula tissues and exudates. Purified anthecotuloide exerted species-specific, concentration-dependent effects on germination, root development, biomass accumulation, and photosynthetic pigment content. P. lanceolata and P. major were the most sensitive species, S. orientale showed intermediate sensitivity, and T. pratense showed trait-dependent responses with weak germination sensitivity. In contrast, A. cotula showed comparatively high self-tolerance, maintaining germination, growth and pigment stability across most treatments.

The detection of anthecotuloide in A. cotula-derived tissues, root exudates and invaded soils, together with its inhibitory effects on co-occurring species, provides mechanistic evidence for soil-mediated chemical interference by A. cotula. These findings support an allelopathic mechanism consistent with the Novel Weapons Hypothesis, but reciprocal and field-based studies are required to validate its role under natural conditions.