Prosopis juliflora is highly recognized for its invasive character and its detrimental effects on plant species due to the release of allelochemicals. From a preliminary investigation, we found that the number of seedlings of P. juliflora is 10-20 folds greater than other shrubby trees encountered in the area. In this research we aimed to assess the allelopathic effects of crude water extracts of P. juliflora on selected Qatari flora. Effects on germination of lettuce seeds indicated strong-dose-dependent allelopathic effects. The results on native Qatari flora showed that seed germination and/or radicle length of: Acacia tortilis, P. cineraria, Sueda aegyptica, Halopeplis perfoliata, and P. juliflora were affected differently due to different treatment levels. While 10% of significant reduction exerted on seed germination of P. cineraria only at higher concentrations (6 - 8 mgml-1), the seed radical length was significantly reduced starting at the lowest concentration (2 mgml-1) and with significant greater reduction at higher concentrations. The seed germination and seed radical length of Sueda aegyptica were significantly decreased (~ 50%) at 4 mgml-1 crude water extract of P. juliflora. Autotoxic effects of P. juliflora were also observed at higher concentrations of 6mgml-1and 8mgml-1. Seed germination of C. imbricatum was significantly reduced after treatment with the leaf-soil leachate of P. juliflora.

The aqueous leaf extract of P. juliflora was also tested on seedlings of native Qatari plants. The seedlings growth of Aeluropus lagopoides, C. imbricatum and Tetraena qatarensis were all impacted upon treatment. The seedling growth and dry biomass of C. imbricatum were significantly declined at higher concentration of 8mgml-1. However, the seedling growth and dry biomass of Tetraena qatarensis were significantly reduced at all treatment concentration levels. P. juliflora is an invasive and has detrimental effects on associated native plants and establishing a proper management plan of this plant is imperative.