Data from: Microbial Mitigation-Exacerbation Continuum: a novel framework for microbiome effects on hosts in the face of stress

A key challenge to understanding microbiomes and their role in ecological processes is contextualizing their effects on host organisms, particularly when faced with environmental stress. One influential theory, the Stress Gradient Hypothesis, might predict that the frequency of positive interactions increases with stressful conditions such that microbial taxa would mitigate harmful effects on host performance. Yet, equally plausible is that microbial taxa could exacerbate these effects. Here, we introduce the "Mitigation-Exacerbation Continuum" as a novel framework to conceptualize microbial mediation of stress. We (1) use this continuum to quantify microbial mediation of stress for six plant species, and (2) test the association between these continuum values and natural species abundance. We factorially manipulated a common stress (allelopathy) and the presence of soil microbes to quantify microbial effects in benign and stressed environments for two critical early life-history metrics, seed germination and seedling biomass. Although we found evidence of both mitigation and exacerbation among the six species, exacerbation was more common. Across species, the degree of microbial-mediated effects on germination explained >80% of the variation of natural field abundances. Our results suggest a critical role of soil microbes in mediating plant stress responses, and a potential microbial mechanism underlying species abundance.解析微生物组（microbiomes）及其在生态过程中的功能，核心挑战之一在于厘清其对宿主生物的影响情境，尤其是在遭遇环境胁迫时。其中颇具影响力的胁迫梯度假说（Stress Gradient Hypothesis）预测，正向互作的频率会随胁迫程度加剧而提升，进而使微生物类群（microbial taxa）缓解宿主性能受到的有害影响。然而，微生物类群也可能加剧这些负面影响，这一假说同样具有合理性。本研究提出「缓解-加剧连续体（Mitigation-Exacerbation Continuum）」这一全新框架，用于阐释微生物对胁迫的介导作用。我们（1）借助该连续体量化6种植物的微生物胁迫介导效应，（2）检验这些连续体数值与物种自然丰度之间的关联。本研究采用析因设计操控一种常见胁迫——化感作用（allelopathy）——与土壤微生物的存在与否，以量化良性与胁迫环境下两种关键早期生活史指标——种子萌发率与幼苗生物量——对应的微生物效应。尽管在6个物种中均观测到缓解与加剧两种效应，但加剧效应更为普遍。跨物种分析显示，微生物介导的种子萌发效应强度可解释野外自然种群丰度80%以上的变异。本研究结果表明，土壤微生物在调控植物胁迫响应中发挥关键作用，同时也揭示了物种丰度背后潜在的微生物调控机制。