Data from: Functional trait differences and trait plasticity mediate biotic resistance to potential plant invaders

1. Biotic resistance represents an important natural barrier to potential invaders throughout the world, yet the underlying mechanisms that drive such resistance are still debated. In theory, native communities should repel both functionally similar invaders which compete for the same resources, and invaders which possess less competitive traits. However, environmental stress, trade-offs across vital rates and competition-induced plastic trait shifts may modify expected competitive outcomes, thereby influencing invasion dynamics. 2. In order to test these theoretical links between trait distributions and biotic resistance, we performed a mesocosm experiment with 25 non-native ornamental species invading native plant communities. Each non-native species was grown with and without the native community under two watering treatments (regular and reduced). We measured biotic resistance as the difference in performance of non-native individuals grown with and without the community in terms of their survival, growth and reproduction. We quantified overall functional dissimilarity between non-native ornamental individuals and native communities based on the combination of plant height, specific leaf area and seed mass. Then, assuming each of these traits is also potentially linked to competitive ability, we measured the position of non-natives on trait hierarchies. While height is positively correlated with competitive ability for light interception, conservative leaf and seed characteristics provide greater tolerance to competition for other resources. Finally, we quantified plastic trait shifts of non-native individuals induced by competition. 3. Indeed, the native community repelled functionally similar individuals by lowering their survival rate. Simultaneously, shorter ornamental individuals with larger specific leaf areas were less tolerant to biotic resistance from the community across vital rates, although the effect of trait hierarchies often depended on watering conditions. Finally, non-natives responded to competition by shifting their traits. Most importantly, individuals with more competitive traits were able to overcome biotic resistance also through competition-induced plastic trait shifts. 4. Synthesis. Our results highlight that both functional dissimilarity and trait hierarchies mediate biotic resistance to ornamental plant invaders. Nevertheless, environmental stress as well as opposing trends across vital rates are also influential. Furthermore, plastic trait shifts can reinforce potential invaders’ competitive superiority, determining a positive feedback.1. 生物抗性（biotic resistance）是全球范围内阻碍潜在入侵物种的重要天然屏障，但其驱动该抗性的内在机制仍存在学术争议。理论上，本地群落应当能够排斥两类入侵物种：一类是争夺相同资源的功能相似入侵种，另一类是具备较弱竞争性状的入侵种。然而，环境胁迫、生活史关键率间的权衡以及竞争诱导的可塑性性状变化，可能改变预期的竞争结果，进而影响入侵动态。 2. 为验证性状分布与生物抗性间的这些理论关联，我们开展了一项中宇宙实验（mesocosm experiment）：以25种非本土观赏植物为入侵对象，入侵本地植物群落。针对每种非本土物种，我们分别设置有本地群落和无本地群落两个实验组，并施加两种浇水处理（常规浇水与减量浇水）。我们以“有/无本地群落时非本土个体的存活、生长及繁殖表现差异”作为生物抗性的量化指标。基于株高、比叶面积（specific leaf area）和种子质量的组合特征，我们量化了非本土观赏植物个体与本地群落间的整体功能差异度。进一步，假设上述每种性状均可能与竞争能力相关，我们测定了非本土物种在性状层级中的相对位置。尽管株高与光捕获相关的竞争能力呈正相关，但保守型叶片与种子特征对其他资源的竞争具有更强的耐受性。最终，我们还量化了竞争诱导的非本土个体的可塑性性状变化。 3. 实验结果证实，本地群落通过降低存活水平来排斥功能相似的入侵个体。同时，株高较矮、比叶面积较大的观赏植物个体，在各生活史关键率层面对群落产生的生物抗性耐受性更弱，不过性状层级的影响往往依赖于浇水条件。最终，非本土物种会通过调整性状来响应竞争。最为关键的是，具备较强竞争性状的个体，还可通过竞争诱导的可塑性性状变化来克服生物抗性。 4. 综合分析。本研究结果表明，功能差异度与性状层级共同调控了观赏植物入侵种所面临的生物抗性。然而，环境胁迫以及各生活史关键率间的相反趋势同样具有重要影响。此外，可塑性性状变化可强化潜在入侵物种的竞争优势，形成正向反馈回路。