Exotic invasive plant species alter ecosystems and locally extirpate native plant species, and by doing so alter community structure. Changes in community structure may be particularly important if invaders promote species with certain traits. For example, the positive effects of most invaders on soil fertility may promote species with weedy traits, whether native or not. We examined the effects of two co-occurring Prosopis congeners, the native P. cineraria and the exotic invader P. juliflora, on species identified as “agricultural weeds” and species that were not agricultural weeds in the United Arab Emirates. When compared to plots in the open, P. cineraria canopies were associated with lower richness and density of non-weeds while having no impact on agricultural weed species. In contrast, there was lower richness and densities of non-weeds under canopies of P. juliflora, but higher densities of agricultural weeds than in the open surrounding the canopies. These patterns associated with Prosopis congeners and understory plant community composition might be due to the much higher litter deposition, if litter is inhibitory, and shallow root biomass under P. juliflora, or the different soil properties that corresponded with the two Prosopis canopies. In general, soils contained more nitrogen under P. juliflora than P. cineraria, and both understories were more fertile than soil in the open. Our results suggest that evolutionary history may play a role in how exotic invasive species may select for some traits over others in plant communities, with an exotic invader potentially creating reservoirs of agricultural weeds.

外来入侵植物物种改变了生态系统并局部灭绝了本地植物物种，并因此改变了群落结构。如果入侵者推广具有某些特征的物种，则社区结构的变化可能尤其重要。例如，大多数入侵者对土壤肥力的积极影响可能会促进具有杂草性状的物种，无论其是否原生。我们研究了两种同时出现的Prosopis同源物种，即本地的P. cineraria和外来的入侵者P. juliflora对在阿拉伯联合酋长国被识别为“农业杂草”的物种和非农业杂草的物种的影响。与露天的桔梗比较冠层与非杂草的丰富度和密度较低相关，而对农业杂草种类没有影响。相比之下，在朱顶李下，非杂草的富集度和密度较低，但与周围的空旷地相比，农业杂草的密度较高。这些与Prosopis同系物和林下植物群落组成相关的模式可能是由于凋落物的沉积更高，如果具有抑制作用，在胡杨假单胞菌下的根系生物量较浅，或者是与两个Prosopis冠层相对应的不同土壤特性所致。一般而言，在朱红色假单胞菌下土壤比瓜果假单胞菌含有更多的氮。，并且两个地下层都比土壤更肥沃。我们的结果表明，进化史可能在外来入侵物种如何选择植物群落中某些特征而不是其他特征方面起作用，而外来入侵者可能会创造出农业杂草的储存库。