PREMISE The novel-weapons hypothesis predicts that some plants are successful invaders because they release allelopathic compounds that are highly suppressive to naïve competitors in invaded ranges but are relatively ineffective against competitors in the native range. For its part, the evolution of enhanced weaponry hypothesis predicts that invasive populations may evolve increased expression of the allelopathic compounds. However, these predictions have rarely been tested empirically. METHODS Here, we made aqueous extracts of roots and shoots of invasive (North American) and native (European) Brassica nigra plants. Seeds of nine species from North America and nine species from Europe were exposed to these extracts. As control solutions, we used pure distilled water and distilled water with the osmotic potential adjusted with polyethylene glycol (PEG) to match that of root and shoot extracts of B. nigra. RESULTS The extracts had a strong negative effect on germination rates and seedling root lengths of target species compared to the water-control. Compared to the osmolality-adjusted controls, the extracts had a negative effect on seedling root length. We found no differences between the effects of B. nigra plant extracts from the invasive vs. native populations on germination rates and seedling root growth of target plant species. Responses were largely independent of whether the target plant species were from the invaded or native range of B. nigra. CONCLUSIONS The results show that B. nigra can interfere with other species through allelochemical interactions, but do not support predictions of the novel-weapons hypothesis and evolution of increased allelopathy.

中文翻译：

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原生和侵入性黑菜的化感作用不支持新型武器假说

前提新武器假说预测一些植物是成功的入侵者，因为它们释放化感化合物，这些化合物对入侵范围内的幼稚竞争者具有高度抑制作用，但对本地范围内的竞争者相对无效。就其本身而言，增强武器假说的演变预测入侵种群可能会进化出化感化合物的表达增加。然而，这些预测很少经过实证检验。方法 在这里，我们制备了入侵（北美）和本地（欧洲）黑菜植物根和芽的水提取物。来自北美的九个物种和来自欧洲的九个物种的种子暴露于这些提取物。作为控制解决方案，我们使用纯蒸馏水和用聚乙二醇（PEG）调节渗透势以匹配黑木根茎提取物的蒸馏水。结果与水对照相比，提取物对目标物种的发芽率和幼苗根长具有强烈的负面影响。与渗透压调整的对照相比，提取物对幼苗根长有负面影响。我们发现来自入侵种群和本地种群的 B. nigra 植物提取物对目标植物物种的发芽率和幼苗根生长的影响没有差异。响应在很大程度上与目标植物物种是来自入侵的黑种草还是本地的黑种树无关。结论 结果表明，B. nigra 可以通过化感作用干扰其他物种，