Dominance of warm-season grasses modulates tallgrass prairie ecosystem structure (e.g., community composition) and function (e.g., net primary production). Seed sources for re-introduction of dominant prairie grass species include native (local remnant ecotypes) and selected (USDA cultivar) populations. The overall objective of this study was to quantify whether intraspecific variation in developing root systems exists between sources (native and cultivar) of three dominant grasses used in restorations: Andropogon gerardii, Sorghastrum nutans, and Schizachyrium scoparium. Native and cultivar sources of each species were grown in 7.62 cm diameter x 20 cm depth PVC cores inserted in a newly established experimental tallgrass prairie restoration at the Konza Prairie Biological Station, Manhattan, KS. We measured above and belowground net primary production (ANPP and BNPP), root architecture, and plant available inorganic nitrogen in each core following in situ incubation for one growing season. Cultivars of S. nutans and S. scoparium had greater BNPP than non-cultivars (P=0.043); no native seedlings of A. gerardii survived the first growing season. Cultivars of S. nutans exhibited greater BNPP than cultivars of A. gerardii (P=0.100) and S. scoparium (P=0.050). Across all species and sources, root systems were comprised of at least 98% fine roots (< 1.0 mm diameter). Soil nitrogen availability was not correlated with root biomass among cultivar or native sources of the dominant grasses. Although root architecture was similar among species and sources, intraspecific and interspecific differences in root production may have consequences for competitive interactions, plant diversity, and recovery of soil organic matter in tallgrass prairie restorations.