Herbicidal Effects and Cellular Targets of Aqueous Extracts from Young Eucalyptus globulus Labill. Leaves

Eucalyptus globulus Labill. is a widespread exotic species that contributes to the formation of fire-prone environments, a great concern under climate change conditions. Therefore, sustainable practices to help locals managing eucalyptus stands are needed. In this perspective, harnessing eucalyptus' specialized metabolism as a source of allelochemicals can be a promising approach for weed control. Thus, the main goals of this work were to evaluate the herbicidal potential of post-fire regenerated E. globulus leaves against Portulaca oleracea L. and to unravel the physiological mechanisms behind this phytotoxic action. For this, aqueous extracts of fresh (FLE; 617 g FW L^-1) or oven-dried leaves (DLE; 250 g DW L^-1) were foliar-sprayed at different dilutions in purslane seedlings. After five weeks, results revealed that DLE at the highest dose detained the greatest herbicidal activity, affecting purslane growth and cellular viability. Moreover, biochemical data pointed towards an overproduction of reactive oxygen species, causing harsh oxidative damage in roots, where the upregulation of important cellular players, like sugars, amino acids, and proline, was not able to reestablish redox homeostasis. Overall, this study proved that dried leaves from young E. globulus had potent herbicidal properties against P. oleracea and can represent a feasible strategy for weed management.