Differences in growth traits betweenChromolaena odorataplants from invasive and native populations

飞机草(Chromolaena odorata) 是我国热带地区危害严重的外来入侵植物,为揭示适应进化对其成功入侵的贡献,在同质种植园中,比较研究了飞机草10 个入侵地种群与12 个原产地种群生长性状的差异,为排除奠基者效应的可能影响,进一步比较了飞机草10 个入侵地种群与其原产地可能的祖先种群间的差异。结果表明,飞机草10 个入侵地种群的基茎、株高、分枝数、生物量和比叶面积均显著高于12 个原产地种群;与可能的祖先种群相比,飞机草10 个入侵种群的生物量、分枝数和比叶面积仍更高。这些结果表明,在长期的入侵过程中飞机草通过进化提高了资源向生长的分配,支持增强竞争能力的进化假说。;Biological invasions are serious socio-economic and environmental problems. Invasion ecology has become one of the hotspots in recent years. However, the mechanisms underlying exotic plant invasions are still not well elucidated, although many related studies have been conducted worldwide. The Evolution of Increased Competitive Ability (EICA) Hypothesis predicts that invasive plant species may decrease resource allocation to defense and therefore increase allocation to growth in response to enemy release in their new ranges. To test this hypothesis, many studies have been carried out in both invasive and native ranges of many introduced plants. Some of these studies do not provide any evidence for the EICA hypothesis, although more studies support this hypothesis. One of the reasons for the inconsistent results is that almost all related studies compared the differences in performance between plants from invasive and native populations in general, without considering the potential influence of founder effect. To exclude the influence of confounding founder effect, we should compare the difference between the plants from invasive populations and the plants from their source native populations. However, the source populations of invasive species are rarely known with certainty. To investigate the role of post-introduction evolution in successful invasion of Chromolaena odorata (L.) King & Robinson (Asteraceae), we compared the overall differences in growth traits between the plants originating from seeds collected in 10 populations in its invasive range in Asia and the plants originating from seeds collected in 12 populations in its native range in America in a common garden. In order to decrease or even exclude the influence of founder effect, we specifically compared the plants from the 10 invasive populations with the plants from their six putative source populations. Chromolaena odorata is native to North, Central, and South America, but a noxious perennial invasive forb or subshrub throughout the tropics in Africa, Asia, and Oceania. It was introduced into Calcutta, India in the middle of the nineteen century. It was first found in Yunnan, southwest China in 1934. Now it occurs in Yunnan, Guangxi, Guizhou, Hainan, Guangdong, Taiwan, Hongkong, and Macao, becoming one of the most noxious invasive plants in China. Chromolaena odorata harbours more than 240 enemies in its native range and 25% of them are specialists to the invader. However, only few generalists were found for the invader in its native range in China. Chromolaena odorata plants invading in Asia may originate from Florida and Trinidad according to the results of studies with molecular markers. In the common garden, C. odorata plants from the 10 invasive populations were significantly higher in stem diameter, plant height, branch number, total biomass, and specific leaf area than the plants from the 12 native populations. Compared with the plants from the six putative source populations, the plants from the 10 invasive populations were also higher in total biomass, branch number, and specific leaf area. Our results indicate that C. odorata appears to have increased resource allocation to growth through post-introduction evolution, providing more convincing evidence for the EICA hypothesis than general comparisons between invasive plants and their native conspecifics without considering their ancestors.