Allelopathic vs. autotoxic potential of a grassland weed—evidence from a seed germination experiment

<b>Background</b>: Mechanisms affecting invasiveness of non-indigenous species have received much attention. Few studies have investigated invasions by native plants. Invasive native species such as common ragwort (<i>Jacobaea vulgaris</i>) may become noxious weeds. They challenge farming and nature conservation by outcompeting fodder plants or rare herbs. One mechanism that can result in outcompeting plants is by allelopathy. <b>Aim</b>: We evaluated the potential of <i>J. vulgaris</i> to suppress germination in common and rare grassland species by allelopathy. <b>Methods</b>: In a germination chamber experiment, we exposed 22 species and <i>J. vulgaris</i> itself to ragwort leachate. We controlled for osmotic effects by germination tests in mannitol solution and water. We assessed germination percentage—time —synchrony and radicle length. <b>Results</b>: Leachate reduced germination percentage, germination time, synchrony and radicle length. These effects were similar for <i>J. vulgaris</i>, indicating autotoxicity. Rare species germinated less than common species but were not more sensitive to the phytotoxic effects of <i>J. vulgaris</i>. Restraining effects of the leachate were similar to the mere osmotic effect. <b>Conclusion</b>: Our results question allelopathy as the main driving mechanism behind <i>J. vulgaris</i> gaining dominance. However, the impact of <i>J. vulgaris</i> might depend on the composition of the invaded plant community due to species-specific effects.

**背景**：影响外来物种入侵性的机制已得到广泛关注，但针对本土植物入侵的研究仍较为匮乏。入侵性本土物种如欧洲千里光（Jacobaea vulgaris）可演变为恶性杂草，通过竞争排挤饲料植物或珍稀草本植物，对农业生产与自然保护造成挑战。其中，化感作用（allelopathy）是导致植物被竞争排挤的潜在机制之一。

**研究目的**：本研究旨在评估欧洲千里光通过化感作用抑制常见与珍稀草原物种种子萌发的潜力。

**实验方法**：本研究采用萌发箱实验，将22种受试植物及欧洲千里光自身暴露于千里光浸提液中；同时设置甘露醇溶液与清水萌发对照实验，以控制渗透效应的干扰。本研究测定了受试物种的萌发率、萌发时间、萌发同步性及胚根长度。

**实验结果**：千里光浸提液可降低受试物种的萌发率、延缓萌发进程、降低萌发同步性并缩短胚根长度；该抑制效应同样存在于欧洲千里光自身，表明其存在自毒作用。珍稀草原物种的整体萌发率低于常见物种，但对欧洲千里光的植物毒性效应并未表现出更高的敏感性。浸提液的抑制效应与单纯渗透效应无显著差异。

**研究结论**：本研究结果对"化感作用是欧洲千里光获得种群优势的核心驱动机制"这一观点提出了质疑。但由于物种特异性效应的存在，欧洲千里光的入侵影响可能取决于被入侵植物群落的物种组成。