Allelopathic potential of Leucaena leucocephala (Lam.) de Wit leaf extracts on native species

Allelopathy is seen as one of the possible factors that favor the invasion of exotic plants in the environment, as these species, by releasing allelochemicals, can negatively interfere with the establishment of native plants, facilitating the growth and dissemination of invasive exotic plants. This study aimed to verify the possible allelopathic effects of Leucaena leucocephala (Lam.) de Wit (leucaena) on native tree species Pterogyne nitens Tul. and Peltophorum dubium (Spreng.) Taub., via laboratory bioassays. We used Petri dishes containing seeds of native species and aqueous extract of leucaena leaves with 2, 4, 8, 10 and 20% concentrations (m/v) for germination tests and estimated the percentage, mean time, and germination speed index at the end of the germination period. For initial growth, we kept the Petri dishes containing aqueous leucaena extract and germinated seeds of native species in a germination chamber at 25 °C, and after 48 hours we obtained the length of the primary root, hypocotyl, and fresh and dry biomass of the seedlings. We obtained the a, b, and total chlorophyll and carotenoid content of seedling leaves kept in the aqueous extract at different concentrations. We verified the content of total phenolic compounds in mg/L from the aqueous leucaena extracts. Both native species showed a reduction in the percentage and germination speed index when in contact with the aqueous leucaena extracts at the highest concentrations. The initial growth of native species was also negatively affected, and P. nitens showed a reduction of all growth parameters analyzed in all concentrations of the aqueous extract. P. dubium showed a reduction in growth, especially at the highest concentrations. The effects can be associated with phenolic compounds present in leucaena extracts, and we found the highest total phenolic content in the extract with the highest concentration. The results show the allelopathic potential of leucaena, which may contribute to this plant ability to settle in natural areas.