Abstract Urban greening may enhance the distribution of exotic species that represent a threat for the native species in new urban systems. Paspalum dilatatum Poir. is one of the exotic naturalized species dominating in gardens of new urban ecosystems in Egypt. This study was conducted to evaluate the allelopathic interference of such species on the native plants in these habitats. The field study showed that the plots infested with Paspalum attained lower coverage, diversity and biomass of native plants than those free from it. Amaranthus viridis and Dactyloctenium aegyptium were completely absent from the sites involving P. dilatatum. Moreover, Paspalum-infested soils were of more water content, available nitrogen and extremely higher nitrogenase activity. In a greenhouse experiment, the rhizosphere soil under Paspalum reduced germination and growth of some native species, namely, Amaranthus viridis, Medicago lupulina, Melilotus indicus and Plantago amplexicaulis. Moreover, growth inhibition was inversely related to the seed size of these tested species. The spectrophotometric analysis revealed that higher contents of phenolics and flavonoids were detected in the Paspalum-infested soils in comparison with free ones. Besides, the high performance liquid chromatographic (HPLC) analysis indicated the presence of some free phenolics and flavonoids with higher concentrations in Paspalum-infested soils. The results indicate that the exotic naturalized P. dilatatum had negative effects on coverage, biomass and diversity of the native species in urban gardens. The obtained inhibition in these criteria was not attributed to soil characteristics. Furthermore, the significant reduction in germination and growth of the target species under greenhouse conditions could be attributed to the higher phenolic and flavonoid contents in the Paspalum-infested soils. These findings suggest that allelopathy had, at least, partial role in the negative impact caused by P. dilatatum. This species may also represent a threat for the native plant communities in new urban ecosystems.

中文翻译：

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异国情调的归化雀稗的化感干扰。威胁到城市花园中本地植物的多样性

摘要 城市绿化可能会增加外来物种的分布，这些物种对新城市系统中的本地物种构成威胁。Paspalum dilatatum Poir。是埃及新城市生态系统花园中占主导地位的外来归化物种之一。本研究旨在评估此类物种对这些栖息地的本地植物的化感作用干扰。田间研究表明，被雀稗侵染的地块的原生植物覆盖率、多样性和生物量低于没有它的地块。Amaranthus viridis 和 Dactyloctenium aegyptium 在涉及 P. dilatatum 的站点中完全不存在。此外，雀稗侵染的土壤含水量更高，有效氮含量更高，固氮酶活性极高。在温室实验中，Paspalum 下的根际土壤减少了一些本地物种的萌发和生长，即 Amaranthus viridis、Medicago lupulina、Melilotus indicus 和 Plantago amplexicaulis。此外，生长抑制与这些测试物种的种子大小成反比。分光光度法分析表明，与游离土壤相比，在雀稗侵染的土壤中检测到更高含量的酚类和黄酮类化合物。此外，高效液相色谱 (HPLC) 分析表明，在雀稗侵染的土壤中存在一些浓度较高的游离酚类和黄酮类化合物。结果表明，外来归化的P. dilatatum对城市花园中本地物种的覆盖度、生物量和多样性有负面影响。在这些标准中获得的抑制作用不归因于土壤特性。此外，温室条件下目标物种的发芽和生长显着减少可归因于雀稗侵染土壤中较高的酚类和类黄酮含量。这些发现表明，化感作用至少在 P. dilatatum 造成的负面影响中起到了部分作用。该物种也可能对新城市生态系统中的本地植物群落构成威胁。