Allelopathic aqueous extract of Ludwigia repens affects the photosynthesis and growth of the invasive Salvinia molesta: implications for aquatic weed management

Allelochemicals are plant secondary metabolites with potential as cost-effective and environmentally friendly tools for managing invasive plant species, yet their potential for controlling aquatic weeds remains underexplored. This study experimentally assessed the allelopathic effects of an aqueous crude extract from stems and leaves of Ludwigia repens , a rooted aquatic macrophyte rich in phenolic allelochemicals —native to North and Central America— on the physiology and growth of Salvinia molesta , a free-floating aquatic weed that has recently spread from its native range (South America) into North America. We hypothesize that the extract of L. repens with a high content of phenolic compounds inhibits the growth and development of S. molesta . After one week of exposure, S. molesta exhibited reduced photosynthetic performance and CO 2 assimilation, resulting in decreased relative growth rate and surface cover. By day 21, however, a substantial recovery was observed, coinciding with the degradation of most phenolic compounds extracted from L. repens . These results show the bioherbicidal potential of L. repens extract, which could be a valuable tool for managing S. molesta when combined with other control methods that limit regrowth. The rapid breakdown of phenolic compounds suggests a low risk of environmental residues of L. repens ’ allelochemicals. Nevertheless, the reduction in dissolved oxygen caused by the oxidation of organic substances in the extract warrants attention due to possible impacts on ecosystem functioning. Further research is required to address key knowledge gaps, particularly regarding the herbicidal efficacy of allelopathic plant extracts in aquatic ecosystems and their effects on non-target species. • Aqueous extract of Ludwigia repens is rich in phenolic compounds. • L. repens extract reduces photosynthetic efficiency and carbon gain in Salvinia molesta. • L. repens extract inhibit the growth of S. molesta. • After three weeks, phenolic degradation allows S. molesta to recover substantially. • Bioherbicidal effects suggest potential in integrated weed management strategies.