Data from: Invasive legumes can associate with many mutualists of native legumes, but usually do not

Mutualistic interactions can strongly influence species invasions, as the inability to form successful mutualisms in an exotic range could hamper a host’s invasion success. This barrier to invasion may be overcome if an invader either forms novel mutualistic associations or finds and associates with familiar mutualists in the exotic range. Here we ask (1) does the community of rhizobial mutualists associated with invasive legumes in their exotic range overlap with that of local native legumes and (2) can any differences be explained by fundamental incompatibilities with particular rhizobial genotypes? To address these questions, we first characterized the rhizobial communities naturally associating with three invasive and six native legumes growing in the San Francisco Bay Area. We then conducted a greenhouse experiment to test whether the invasive legume could nodulate with any of a broad array of rhizobia found in their exotic range. There was little overlap between the Bradyrhizobium communities associated with wild-grown invasive and native legumes, yet the invasive legumes could nodulate with a broad range of rhizobial strains under greenhouse conditions. These observations suggest that under field conditions in their exotic range, these invasive legumes are not currently associating with the mutualists of local native legumes, despite their potential to form such associations. However, the promiscuity with which these invading legumes can form mutualistic associations could be an important factor early in the invasion process if mutualist scarcity limits range expansion. Overall, the observation that invasive legumes have a community of rhizobia distinct from that of native legumes despite their ability to associate with many rhizobial strains, challenges existing assumptions about how invading species obtain their mutualists. These results can therefore inform current and future efforts to prevent and remove invasive species.

互利共生相互作用（mutualistic interactions）可显著影响物种入侵过程：若宿主无法在外来分布区形成成功的互利共生关系，则其入侵成功率将受到阻碍。若入侵物种能在外来分布区形成全新的互利共生关联，或是觅得并结合熟悉的互利共生伙伴，则可突破这一入侵障碍。
本研究旨在解答两个科学问题：其一，在外来分布区与入侵豆科植物（invasive legumes）相关联的根瘤菌互利共生群落，是否与本地原生豆科植物的根瘤菌群落存在重叠？其二，群落间的差异是否可通过与特定根瘤菌基因型（rhizobial genotypes）的根本性不相容性来解释？
为解答上述问题，本研究首先对生长于旧金山湾区的3种入侵豆科植物与6种原生豆科植物的自然关联根瘤菌群落进行了表征。随后，本研究开展了温室盆栽实验，以验证入侵豆科植物能否与外来分布区中发现的广泛类群根瘤菌形成结瘤关系。
野生状态下，与入侵豆科植物和原生豆科植物相关联的慢生根瘤菌属（Bradyrhizobium）群落几乎不存在重叠；但在温室条件下，入侵豆科植物可与广泛类群的根瘤菌菌株（rhizobial strains）形成结瘤。上述观测结果表明，尽管入侵豆科植物具备形成此类关联的潜力，但在外来分布区的野外条件下，它们目前并未与本地原生豆科植物的互利共生伙伴形成关联。
但若互利共生伙伴的稀缺性限制了种群扩张，那么这些入侵豆科植物形成互利共生关联的广谱性，可能是入侵早期的关键影响因素。总体而言，尽管入侵豆科植物可与多种根瘤菌菌株形成关联，但其根瘤菌群落与原生豆科植物截然不同——这一观测结果对现有关于入侵物种如何获取互利共生伙伴的理论假设提出了挑战。因此，本研究结果可为当前及未来的外来入侵物种防控工作提供参考依据。