IntBIO Collaborative Research: Assessing drivers of the nitrogen-fixing symbiosis at continental scales

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Nitrogen is an essential nutrient for all life on earth. It is also the most abundant element in the atmosphere, but most organisms cannot access it from the air directly. Only certain specialized microbes have the ability to convert nitrogen in the atmosphere into a biologically useful form in a process known as nitrogen fixation. Some of these microbes are free-living, but most live in a close symbiotic association within the roots of plants, exchanging nitrogen for carbon. This nitrogen-fixing symbiosis is a central component of the global nitrogen cycle, and it is central to agricultural systems because nitrogen is often the limiting factor for crop growth. It is therefore imperative to understand how nitrogen-fixing plant-bacterial partnerships form in nature and how they respond to an environment filled with challenges and in constant flux. The purpose of this project is to provide a data-intensive framework to learn how plants and bacteria choose their partners and how this choice influences and responds to surrounding species, soil, and climate. A second purpose of the project is to train students from groups underrepresented in science. Students will be prepared for the data-intensive careers now needed across STEM disciplines using an innovative mentorship program and interdisciplinary research including fieldwork, laboratory work, and computational biology.The project will investigate the diversity of nitrogen-fixing bacteria and other microbes associating with plant roots across the North American continent using NSF-sponsored ecological monitoring resources through NEON (the National Ecological Observatory Network). At each of 45 NEON sites, environmental data will be combined with data on the nitrogen-fixing symbiosis. Specifically, investigators will sample the microbiome in the soil and root nodules, and will assay leaf isotopes to determine the level of function of nitrogen-fixing symbionts. Leveraging data from these different sources, the PIs will be able to determine whether microorganisms and plant partners are each limited by the same environmental factors, such as aridity. They will also be able to determine the extent to which choosiness of plant or microbe partners limit the extent of the association. In addition, by examining patterns in the tree of life, the PIs will be able to infer whether highly specific partnerships have persisted across evolutionary time. Finally, models will be used to address synthetic questions across all data sources. For example, a model can test the prediction that arid environments favor highly specific associations, in which both microbes and plants choose specific partners in those stressful settings.This project is jointly funded by the BIO Emerging Frontiers Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.