Improving nitrogen use efficiency is essential for sustainable agricultural production. Nitrogen use efficiency is low because it is an inherently complex systems property governed by multiple interacting genetic and environmental factors. The pathway for plant nitrogen uptake is initiated in the rhizosphere where interactions between roots, microbes, and soil create a complex interplay influencing the timing, amount, and chemical form of nitrogen that is available to the plant. The inability of maize to efficiently use nitrogen is also linked to past plant breeding strategies that have selected genotypes that flourish with large synthetic nitrogen fertilizer inputs, which is reflected by a reduction in the extent to which roots exploit soil nitrogen resources. In soils rich in organic matter, like those in the Midwest Corn Belt, much of the biologically available nitrogen is tied up in the organic matter.To achieve high yields with low fertilizer inputs requires identifying germplasm that stimulates microbial metabolic activities to liberate the nitrogen sequestered in the soil organic matter, and more efficiently deliver nitrogen to maize. This project will exploit a diverse set of high-nitrogen use efficiency germplasm derived from exotic maize landrace accessions integrated into a temperate inbred line and a long-term nitrogen fertilizer rate experiment that has created gradients in soil properties and microbial communities. Our goal is to determine whether high-nitrogen use efficiency genotypes select for a rhizosphere microbial community whose metabolic activities are better at liberating the nitrogen sequestered in the soil organic matter and more efficiently deliver nitrogen to maize. We will also assess whether high-nitrogen use efficiency genotypes are better able to directly acquire nitrogen from soil through their interactions with microbes.The specific objectives of our project are to 1) assess how high-nitrogen use efficiency maize germplasm influences rhizosphere and endophytic microbiome assembly, 2)quantify how high-nitrogen use efficiency maize germplasm influences rhizosphere nitrogen-transformations, and 3)assess how maize root properties are influenced by genotype and nitrogen-fertilization.By coupling descriptions of the root microbiome, N-transformations, and root properties with metabolite profiling of root exudates/secretions we will develop models to determining whether rhizosphere priming may shape the microbiome.