Cultivars of dominant C₄ grasses, selected for characters such as high productivity and stress tolerance, are commonly used in tallgrass prairie restorations despite potential physiological dissimilarity to local seed sources. Since dominant species play crucial roles in community structure and ecosystem function, population source of dominant C₄ grasses may have consequences for diversity, productivity, and ultimately success of grassland restorations. We tested whether intraspecific variation in physiology and productivity existed between cultivar and non-cultivar population sources of dominant prairie grasses (Andropogon gerardii, Sorghastrum nutans, and Schizachyrium scoparium) during the second year of an experimental prairie restoration. Net photosynthesis (A_net) and stomatal conductance (g_s) were measured 4 times during the growing season and above-ground net primary production (ANPP) was measured at the end of the growing season prior to senescence. Water use efficiency (WUE) was calculated as the ratio net photosynthesis to transpiration to determine the amount of carbon gained per unit of water lost. 
Results/Conclusions

Rates of A_net were 17-31% higher in cultivar population sources across the three species (p < 0.001). Cultivars of A. gerardii and S. nutans exhibited 14-25% higher rates of g_s than non-cultivars (p < 0.01). Cultivars of A. gerardii and S. scoparium showed 9-14% higher WUE than non-cultivars (p < 0.01). Finally, cultivars of A. gerardii and S. scoparium exhibited higher ANPP than non-cultivars (p = 0.05). Our results demonstrate enhanced physiological performance and productivity in cultivars of dominant prairie grasses widely used in tallgrass prairie restorations. Therefore, population seed source should be considered as a potential filter on ecosystem re-assembly during restoration.