Data from: Reduced mycorrhizal responsiveness leads to increased competitive tolerance in an invasive exotic plant

1. Arbuscular mycorrhizal (AM) fungi can exert a powerful influence on the outcome of plant-plant competition. Since some exotic plants interact differently with soil biota such as AM fungi in their new range, range-based shifts in AM responsiveness could shift competitive interactions between exotic and resident plants, although this remains poorly studied. 2. We explored whether genotypes of the annual exotic Centaurea solstitialis (yellow starthistle), collected from populations across the native and non-native ranges, differed in responsiveness to AM fungi in the introduced range and whether range-based differences in mycorrhizal responsiveness affected how strongly C. solstitialis tolerated competition with the North American native bunchgrass, Stipa pulchra. 3. Grown alone, C. solstitialis from both ranges derived only weak benefits from AM fungi. However, association with AM fungi was costly to plants when grown in competition with S. pulchra. The magnitude of the suppressive effect of AM fungi was greater for genotypes from native versus introduced populations. 4. Synthesis. Many exotic invasive species are known to associate weakly with AM fungi, which may be beneficial in disturbed habitats where competition for resources is low. Our results indicate that reduced mycorrhizal associations may also benefit invaders in a competitive environment. C. solstitialis had lower competitive tolerance in the presence versus absence of AM fungi, but native genotypes had lower tolerance than exotic genotypes. This suggests that AM fungi may contribute to invasion resistance in established native communities, but range-based shifts in the way exotic genotypes respond to AM fungal partners may counter such biotic resistance.

1. 丛枝菌根（Arbuscular mycorrhizal, AM）真菌可对植物间竞争的结局产生显著影响。由于部分外来植物在入侵新分布区后，与丛枝菌根真菌这类土壤生物群落的互作模式会发生改变，因此丛枝菌根响应性的分布区差异可能会改变外来植物与本地植物间的竞争互作模式，不过目前针对该议题的研究仍较为匮乏。
2. 本研究旨在探讨两个核心科学问题：一是从原生分布区与非原生分布区种群中采集的一年生外来入侵植物黄星蓟（Centaurea solstitialis）的不同基因型，在入侵分布区中对丛枝菌根真菌的响应是否存在差异；二是基于分布区的菌根响应性差异是否会影响黄星蓟对北美本地丛生禾草美丽针茅（Stipa pulchra）的竞争耐受能力。
3. 单独栽培时，来自两个分布区的黄星蓟仅能从丛枝菌根真菌的共生关系中获得微弱的生长收益。但当与美丽针茅共同栽培时，与丛枝菌根真菌建立共生关系反而会给植株带来生长代价。且相较于来自入侵分布区的基因型，来自原生分布区的基因型受丛枝菌根真菌的抑制效应更为显著。
4. 研究总结：已知许多外来入侵物种与丛枝菌根真菌的共生关系较弱，这在资源竞争程度较低的受干扰生境中或许是有益的。本研究结果表明，减弱的菌根共生关系或许同样能让入侵物种在竞争环境中获益。相较于无丛枝菌根真菌的情境，黄星蓟在有丛枝菌根真菌存在时的竞争耐受能力更低，且原生分布区来源的基因型的竞争耐受能力要低于入侵分布区来源的基因型。这提示丛枝菌根真菌可能会在已建立的本地植物群落中促进生物入侵抵抗能力，但外来基因型对丛枝菌根真菌伙伴的响应模式所发生的分布区偏移，或许会抵消这类生物抵抗效应。