豚草（Ambrosia artemisiifolia L.）在中国的入侵据记载已有近90年，目前在东北、华北、华中、华东都有大面积分布，其与本地土著种的竞争是入侵过程中不可缺失的一环。作为外来入侵植物，一般认为豚草具有更强的种间竞争能力，这也是它成功入侵的关键。豚草与本地土著种的竞争关系可能受到外界环境条件变化的影响，而酸雨是国内常见的一个环境问题，对不能移动的植物有着直接的作用。故本研究以北京市门头沟地区考察到的豚草和伴生土著种鬼针草（Bidens bipinnata L.）为研究对象，进行单一种植和多比例混合种植开展de Wit替代竞争实验，并施加不同浓度的酸雨模拟溶液，来探究酸雨对入侵种豚草和伴生种鬼针草竞争关系的影响。研究结果显示，在单一种植时，中浓度酸雨促进了入侵植物和本地植物的早期生长，但高浓度酸雨对入侵豚草早期营养生长具有显著的抑制作用，后期抑制作用减弱；在混合种植时，由于豚草产生的种间竞争抑制和整个生长季酸雨的抑制，生长季结束时，高浓度酸雨环境下土著种鬼针草的株高显著降低；豚草在高密度环境下相对于土著种鬼针草表现出了明显的竞争优势，酸雨的出现全面增强了豚草的种间竞争优势。本研究揭示了环境因子的改变对入侵植物与本土植物的竞争关系的影响。

The invasion of common ragweed (Ambrosia artemisiifolia L.) in China has a long history for nearly 90 years. It is widely distributed in Northeast, North, Central and East China. As an invasive plant, ragweed has been thought to have stronger interspecific competition ability, which promotes its successful invasion. The competition between common ragweed and indigenous species may be influenced by the changes of environmental conditions, and acid rain is a common environmental problem in China, which has a direct effect on immobile plants. In this study, the common ragweed and the accompanying indigenous species bidens (Bidens bipinnata L.) in Mentougou District of Beijing were used as the research objects, and the de Wit replacement competitive experiment was performed by single planting and multi-proportion mixed planting. The effects of acid rain on the competition interaction between invasive common ragweed and its accompanying indigenous bidens were studied by applying different concentrations of simulated acid rain solution (pH=3, pH=4, pH=5) on them. The results showed that the medium level concentration of acid rain promoted the early growth of invasive and indigenous plants, but the high level concentration of acid rain inhibited the early growth of invasive common ragweed. Due to the inhibition of interspecific competition caused by ragweed and acid rain during the whole growing season, the plant height of bidens, which were cultivated in the high level of acid rain environment, decreased significantly at the end of the growing season in mixed planting. When planted in high density, common ragweed showed obvious competitive advantage over indigenous bidens. The occurrence of acid rain enhanced both interspecific and intraspecific competition in common ragweed.