Origins and impacts of nitrogen-fixing symbioses in a major clade of flowering plants

所有的生物都需要氮来生长，但是大气中的氮并不是大多数物种都能直接获得的，必须首先转化为适合使用的形式。豆类，如豌豆、扁豆和大豆，以及其他一些开花植物群体可以与固氮细菌形成共生关系，并将它们安置在根部，以换取可用的氮。这种共生关系对生态系统功能和农业生产力至关重要。尽管理解这种相互作用具有很强的价值，但科学家们尚未揭示这种共生关系是如何进化的，以及它对全球开花植物多样性的长期进化影响。该项目将通过解决15000种有花植物固氮物种的进化关系，分析与细菌共生相关的基因，并将这些新知识与物种栖息地和形态特征的综合数据库联系起来，从而缩小这一差距。研究人员将通过针对高中、本科和研究生水平的生物学前沿数据科学方法研讨会来建立科学能力。向公众宣传将提高人们对生命之树中有机共生的重要性的认识，以及对这些关系的了解如何能够加强粮食安全和人类福祉。研究人员将通过测试四个主要假设来评估被子植物与固氮细菌共生关系的宏观进化后果。细菌共生是否使植物物种能够入侵新的、更恶劣的低氮土壤环境？如果是这样，是否获得了其他植物特性，使植物能够应对这些极端的栖息地？细菌共生关系的增加是否使这些植物群比没有这种关系的植物群更快地进化出新的物种？全球气候在地质时期的变化，包括寒冷和干燥栖息地的扩散以及大气中二氧化碳水平的下降，是否推动了细菌共生的近期进化？研究人员将利用来自约230个核位点的序列数据，重建被子植物固氮进化支的时间校准系统发育框架，并开发一套生物多样性信息学方法，以大规模生成物种分布模型和功能性状矩阵。然后，研究人员将使用比较方法分析这些数据。研究结果将提供一个严谨的生态和进化因素，推动这种共生关系的得失，以及结瘤本身如何影响被子植物的多样化和全球分布。该项目开发的方法将促进未来的综合分析，利用广泛的系统发育、空间和时间尺度上丰富的、精心策划的数据资源。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

All living organisms require nitrogen to grow, but atmospheric nitrogen is not directly available to most species and must first be converted into a form suitable for use. Legumes, such as peas, lentils, and soybeans, and several other flowering plant groups can form symbiotic relationships with nitrogen-fixing bacteria and house them in their roots in return for access to usable nitrogen. This symbiotic relationship is essential to ecosystem functioning and agricultural productivity. Despite the strong value in understanding this interaction, scientists have yet to unravel how this symbiosis evolved and its long-term evolutionary consequences for the global diversity of flowering plants. This project will close this gap by resolving the evolutionary relationships of 15,000 nitrogen-fixing species of flowering plants, analyzing the genes associated with their bacterial symbioses, and linking this new knowledge to a comprehensive database of species' habitat and morphological traits. Researchers will build scientific capacity through workshops on cutting-edge data science approaches in biology, targeting high school, undergraduate, and post-graduate levels. Outreach to the general public will increase awareness of the importance of organismal symbioses across the tree of life and how knowledge about these relationships can enhance food security and human well-being. Researchers will evaluate the macroevolutionary consequences of angiosperms' symbiotic relationships with nitrogen-fixing bacteria by testing four overarching hypotheses. Did bacterial symbiosis enable plant species to invade new, harsher soil environments low in nitrogen? If so, were other plant traits gained that allowed the plants to cope with these extreme habitats? Did the gain of bacterial symbioses allow these plant groups to evolve new species more rapidly than those without this relationship? Did global climate change over geologic time, including the spread of colder and drier habitats and falling atmospheric carbon dioxide levels, drive recent evolution of bacterial symbiosis? Researchers will use sequence data from ca. 230 nuclear loci to reconstruct a time-calibrated phylogenetic framework for the nitrogen-fixing clade of angiosperms and develop a suite of biodiversity informatics methods to generate species-distribution models and functional trait matrices at scale. Researchers will then analyze these data using comparative methods. Outcomes of the research will provide a rigorous understanding of the ecological and evolutionary factors that drove the gains and losses of this symbiosis through time and of how nodulation has itself impacted the diversification and global distribution of angiosperms. Methods developed by the project will facilitate future synthetic analyses utilizing rich, curated data resources across broad phylogenetic, spatial, and temporal scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.