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

该奖项将为多年生牧草的生物固氮提供新的见解。固氮是指微生物将大气中的氮气转化为植物可以用来制造蛋白质、DNA和其他对生命至关重要的化合物的形式的过程。这一过程在豆科植物中有充分的记录，即在根瘤中容纳固氮细菌的植物，但它也可能发生在草类中，其中广泛的细菌似乎通过一种称为结合固氮的过程来固定氮。结合固氮的许多细节仍然未知，包括其生态系统的重要性，固定氮的微生物类群，以及驱动其发生的生态关系。结合固氮对许多生态系统具有潜在的意义，在农业上，它可能有助于满足多年生牧草和生物能源对肥料的需求。如果多年生牧草能够从生物固定中获得大部分氮，它就减少了对合成肥料的需求，这既降低了农民的成本，也减少了与使用合成肥料相关的负面环境后果。本研究的目的是确定多年生禾本科植物中伴生固氮发生的时间和数量，确定固氮微生物类群，探讨植物与固氮微生物之间的关系。该项目还将为K-12教师和学生提供研究经验和编写教材。这项研究将使用稳定同位素示踪剂来追踪柳枝稷中的氮，柳枝稷是一种原产于北美草原的多年生草本植物，研究得很好。他们将在柳枝稷组织和周围的土壤中，以及固氮微生物分类群的DNA中，追踪标记过的二氮气体。碳将从植物的光合作用中被追踪到微生物中，这将显示固氮微生物是从植物还是从土壤中吸收碳。最后，将对活性固氮微生物进行测序，由此获得的基因组数据将为植物微生物组的功能提供见解。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。

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.