The potential role of allelopathy in the persistence of invasive weeds

The persistence of weeds is directly influenced by their capacity to interfere with other plants, either through competition for resources or through chemical interference mediated by plant-produced secondary metabolites, a phenomenon known as allelopathy. Recent research has focused on critically assessing the role of allelochemicals in plant succession and invasion, in both native and invaded ecosystems and their associations with other plants and the soil microbiome. The use of sensitive and accurate metabolomics and advanced genomics platforms has led to new advances in the identification of allelochemicals and biotic interactions, biosynthetic pathways associated with their production, and determination of specific impacts on target plant species. In this chapter, we describe the chemistry, biosynthesis, and modes of action of selected groups of allelochemicals associated with persistent and invasive plants and the biotic and abiotic stressors regulating allelochemical production and release. Selected case studies of persistent weeds of global significance exhibiting significant production of allelochemicals are presented, which include the following species: (i) Echium plantagineum, (ii) Centaurea solstitialis, (iii) Sorghum halepense, (iv) Reynoutria japonica, and (v) Parthenium hysterophorus. The use of metabolic profiling technologies has enhanced opportunities for identification and study of the biological activity of these invasive weeds and associated organs, with respect to biosynthesis, persistence, and mode of action. The future profiling of allelochemicals in rhizosphere soils will also provide additional proof of concept of the impact of allelochemicals on microbial diversity and establishment of invasive plants in novel ecosystems.