The recent discovery of a maize landrace from Oaxaca, Mexico, harboring bacteria in the mucilage of its aerial roots that fix significant amounts of nitrogen (N or N2) for plant uptake opens new basic and applied research opportunities for enhancing nutrient use efficiency.This novel phenomenon may have played an important role during the domestication of maize within low input systems. Moreover, N2 fixation has the potential to benefit future farmers and society, since minimizing the inorganic N fertilizer needs in agroecosystems could reduce input costs and environmental and human health consequences stemming from off-site pollution. Replacement of energy inefficient inorganic forms of N could also mitigate climate change. Yet aerial root growth, mucilage production, fixation of N2, and update of fixed N2 can be seen as links in the chain that have may have evolved over time and space, thereby influencing agroecosystem function. We have much to learn about the ability to fix N2 in diverse germplasm representative of maize domestication, spread, and improvement, the role of wild progenitors in conferring these traits, and the importance of N2 fixation for enhancing productivity in the field. Our global goal is to investigate the ways that crop evolution has affected the ability of maize to support atmospheric N2 fixation and benefit from the resulting N. In particular, we will study the following:OBJECTIVE I: Discern how wild Zea taxa vary in their ability to produce aerial roots and mucilage, to perform N2 fixation, and to take up the resulting N.OBJECTIVE II: Determine the structure of quantitative variation among and within wild, landrace, heirloom, and hybrid maize accessions from the US, Mexico, and South America in their ability to produce aerial roots and mucilage, to perform N2 fixation, and take up fixed N.OBJECTIVE III: Determine the effect of aerial root and mucilage production, N2 fixation, and fixed N uptake on productivity of highland and lowland landraces in a maize diversity hotspot.By performing experiments on diverse accessions of maize from across the Americas, we expect to establish a fundamental ecological understanding of how crop evolution has affected N2 fixation and uptake in maize, as well as the traits (aerial roots and mucilage) that promote it. The overarching goal is to understand how the suite of traits that result in biological N fixation on maize aerial roots may enhance agroecosystem function by reducing or eliminating the need for inorganic N fertilization in maize cultivation.