Collaborative Research: The ecological significance of nitrogen fixation in perennial grasses

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This award will provide new insights into biological nitrogen fixation in perennial grasses. Nitrogen fixation is the process by which microbes convert nitrogen gas in the atmosphere to a form that can be used by the plant to make proteins, DNA, and other compounds crucial for life. This process is well-documented for legumes, i.e. plants that house nitrogen-fixing bacteria in root nodules, but it can also occur for grasses where a wide range of bacteria appear to fix nitrogen by a process known as associative nitrogen fixation. Many details of associative nitrogen fixation remain unknown, including its ecosystem importance, the microbial taxa that fix the nitrogen, and the ecological relationships driving its occurrence. Associative nitrogen fixation has potential significance for many ecosystems, and in agriculture it may help to meet the fertilizer requirements of perennial grasses grown for forage and bioenergy. If perennial grasses could get most of their nitrogen from biological fixation, it reduces the need for synthetic fertilizers, which reduces both costs to farmers and the negative environmental consequences associated with synthetic fertilizer use. The goals of this research are to determine when and how much associative nitrogen fixation occurs in perennial grasses, identify the microbial taxa fixing nitrogen, and explore the relationship between the plant and nitrogen-fixing microbes. The project will also provide research experiences and develop teaching materials for K-12 teachers and students. The research will use stable isotope tracers to trace the nitrogen in switchgrass, a well-studied perennial grass native to North American prairies. They will trace labeled dinitrogen gas into switchgrass tissues and surrounding soils, as well as into the DNA of the nitrogen-fixing microbial taxa. Carbon will be traced from photosynthesis through the plant and into microbes, which will show whether the nitrogen-fixing microbes are receiving carbon from the plant or from the soil. Finally, the active nitrogen-fixing microbes will be sequenced, with the resultant genomic data providing insights into the functions of the plant microbiome.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.