Comparative allelopathic potential and phytochemical profiling of invasive and non-invasive alien species of Amaranthus

For invasion biologists, the key question as to why only some alien species emerge as successful invaders as against a majority of other alien introduced species is still unclear. One of the best ways to resolve this question is to compare phylogenetically related alien invasive vs alien non-invasive species. Here we compared the allelopathic potential and phytochemical profiling of two congeneric species of Amaranthus (Amaranthus caudatus-invasive alien and non-invasive alien Amaranthus blitum. Petri dish bioassay followed by a pot experiment was used to evaluate the allelopathic effects of aqueous leaf and root extracts (1:10 w/v) of the said alien congeners on the germination and shoot length of Raphanus sativus. Petri dish bioassay results revealed that both species exhibited comparable levels of allelopathic activity; however, leaf extracts of both species showed significantly stronger inhibitory effects than root extracts, a trend corroborated by phenolic content assessments. However, no allelopathic effects on seed germination were observed in the pot culture bioassay. Comparative phytochemical profiling of these Amaranthus species, utilizing Gas Chromatography-Mass Spectrometry (GC-MS) and High-resolution liquid chromatography and mass spectrometry (HR-LC-MS) identified diverse array of compounds including methyl 8,9-octadecadienoate, n-hexadecanoic acid, phytol, loliolide, stigmasta-7,16-dien-3-ol, catechol borane, ellagic acid etc. which are known for their role in allelopathic interactions and invasiveness of the alien plants. Phytochemical analysis unveiled comparable levels of phytochemicals in both the invasive alien and non-invasive alien species of Amaranthus. In conclusion, our study revealed that while allelopathy may contribute to the invasiveness of the Amaranthus species, it does not seem to be a unique characteristic feature for the invasiveness of invasive alien species (Amaranthus caudatus) in comparison with its non-invasive alien congener. The present study recommends that more congeneric comparisons are needed to understand the role of high chemical diversity in alien plant invasions, and whether it is linked to the origin of the plant species. [GRAPHICS] .