Aims

Understanding the contributions of abiotic and biotic conditions to soil microbial diversity, structure, and function, remains a central focus in soil biology and biogeochemistry. Here we aim to determine how geography and host plant identity influence these different components of rhizosphere bacterial communities and endosymbionts associated with Acacia heterophylla on Réunion island (Mascarene archipelago, Indian Ocean) and A. koa in the Hawaiian Islands (Hawaiian archipelago, Pacific Ocean). These two tree species are remarkable: they are each other’s closest living relatives despite their habitats being more than 16 000 km apart.

Methods

Using 16S rRNA amplicon next-generation sequencing data we show that the structure of rhizosphere communities of these two acacias is largely driven by dispersal limitation between sites and local soil chemical conditions within sites.

Results

Despite high taxonomic turnover in soils collected from different sites, we found their predicted functions to be largely similar, suggestive of functional redundancy. We also identify a core of rhizosphere taxa associated with both Acacia species in both archipelagos, which included potential nitrogen-fixing mutualists. Isolation and characterisation of rhizobia from root nodules of both acacias further supported strong selection by these plants for the same Bradyrhizobium endosymbionts.

Conclusions

Overall, our data suggest that phylogenetically-closely related plants may show remarkably similar selectivity for bacterial mutualists over vast geographic distances.

中文翻译：

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根际细菌分类群的核心与世界上两个最孤立的植物同源物有关

宗旨

了解非生物和生物条件对土壤微生物多样性、结构和功能的贡献，仍然是土壤生物学和生物地球化学的中心焦点。在这里，我们的目标是确定的地理和寄主植物的身份如何影响与相关的根际细菌群落和共生的这些不同组件相思太子参在留尼旺岛（马斯克林群岛，印度洋）和A. KOA在夏威夷群岛（夏威夷群岛，太平洋） . 这两种树种非常了不起：尽管它们的栖息地相距超过 16 000 公里，但它们是彼此最亲近的亲戚。

方法

我们使用 16S rRNA 扩增子下一代测序数据表明，这两种金合欢根际群落的结构很大程度上是由站点之间的扩散限制和站点内当地土壤化学条件驱动的。

结果

尽管从不同地点收集的土壤分类周转率很高，但我们发现它们的预测功能在很大程度上相似，表明功能冗余。我们还确定了与两个群岛中的两种金合欢属相关的根际分类群的核心，其中包括潜在的固氮互惠者。从两种金合欢根瘤中分离和鉴定根瘤菌进一步支持了这些植物对相同慢生根瘤菌内共生菌的强烈选择。

结论

总体而言，我们的数据表明，系统发育密切相关的植物可能在广阔的地理距离内对细菌共生者显示出非常相似的选择性。