Data from: Tradeoffs, spatial heterogeneity, and the maintenance of microbial diversity

Specialization and concomitant tradeoffs are assumed to underlie the non-neutral coexistence of lineages. Tradeoffs across heterogeneous environments can promote diversity by preventing competitive exclusion. However, the importance of tradeoffs in maintaining diversity in natural microbial assemblages is unclear, as tradeoffs are frequently not detected in artificial evolution experiments. Stressful conditions associated with patches of heavy-metal enriched serpentine soils provide excellent opportunities for examining how heterogeneity may foster genetic diversity. Using a spatially-replicated design, we demonstrate that rhizobium bacteria symbiotic with legumes inhabiting contrasting serpentine and non-serpentine soils exhibit a tradeoff between a genotype’s nickel tolerance and its ability to replicate rapidly. Furthermore, we detected adaptive divergence in rhizobial assemblages across soil type heterogeneity at multiple sites, suggesting that this tradeoff may promote the coexistence of phenotypically distinct bacterial lineages. Tradeoffs and adaptive divergence may be important factors maintaining the tremendous diversity within natural assemblages of bacteria.特化及其伴随的权衡（tradeoff）被认为是细菌谱系非中性共存的底层机制。异质环境下的权衡可通过阻止竞争排除（competitive exclusion）来促进物种多样性。然而，权衡在维持自然微生物群落（natural microbial assemblages）多样性中的作用仍不明确，因为在人工进化实验（artificial evolution experiments）中常常无法检测到此类权衡。富重金属蛇纹岩土壤（heavy-metal enriched serpentine soils）生境中的胁迫环境，为探究环境异质性如何推动遗传多样性提供了绝佳研究契机。本研究采用空间重复设计（spatially-replicated design），证实了栖息于截然不同的蛇纹岩与非蛇纹岩土壤中的豆科植物共生根瘤菌（rhizobium），其基因型在镍耐受性与快速繁殖能力之间存在权衡。此外，我们在多个样点的土壤类型异质性梯度中，检测到根瘤菌群落（rhizobial assemblages）存在适应性分化（adaptive divergence），这表明该权衡或许能够推动表型各异的细菌谱系共存。权衡与适应性分化或许是维持自然细菌群落极高多样性的关键因素。