PREMISE Nutrients, light, water, and temperature are key factors limiting the growth of individual plants in nature. Mutualistic interactions between plants and microbes often mediate resource limitation for both partners. In the mutualism between legumes and rhizobia, plants provide rhizobia with carbon in exchange for fixed nitrogen. Because partner quality in mutualisms is genotype-dependent, within-species genetic variation is expected to alter the responses of mutualists to changes in the resource environment. Here we ask whether partner quality variation in rhizobia mediates the response of host plants to changing light availability, and conversely, whether light alters the expression of partner quality variation. METHODS We inoculated clover hosts with 11 strains of Rhizobium leguminosarum that differed in partner quality, grew plants under either ambient or low light conditions in the greenhouse, and measured plant growth, nodule traits, and foliar nutrient composition. RESULTS Light availability and rhizobium inoculum interactively determined plant growth, and variation in rhizobium partner quality was more apparent in ambient light. CONCLUSIONS Our results suggest that variation in the costs and benefits of rhizobium symbionts mediate host responses to light availability and that rhizobium strain variation might more important in higher-light environments. Our work adds to a growing appreciation for the role of microbial intraspecific and interspecific diversity in mediating extended phenotypes in their hosts and suggests an important role for light availability in the ecology and evolution of legume-rhizobium symbiosis.

中文翻译：

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光照可用性和根瘤菌变异相互作用介导豆科植物-根瘤菌共生的结果

前提 养分、光、水和温度是限制自然界中单个植物生长的关键因素。植物和微生物之间的相互影响通常会调节双方的资源限制。在豆科植物和根瘤菌之间的共生关系中，植物为根瘤菌提供碳以换取固定氮。因为共生中的伴侣质量是基因型依赖的，物种内遗传变异预计会改变共生对资源环境变化的反应。在这里，我们询问根瘤菌中的伙伴质量变化是否介导宿主植物对变化的光可用性的反应，相反，光是否会改变伙伴质量变化的表达。方法 我们用 11 株豆科植物根瘤菌接种三叶草宿主，它们的伴侣质量不同，在温室中的环境或弱光条件下种植植物，并测量植物生长、根瘤性状和叶面营养成分。结果光的可用性和根瘤菌接种物相互作用决定了植物的生长，并且根瘤菌伴侣质量的变化在环境光下更为明显。结论我们的结果表明，根瘤菌共生体的成本和收益的变化介导了宿主对光照的反应，并且根瘤菌菌株的变异在高光环境中可能更重要。我们的工作增加了人们对微生物种内和种间多样性在介导宿主扩展表型中的作用的日益认识，并表明光可用性在豆科植物 - 根瘤菌共生的生态学和进化中的重要作用。