Technical Abstract: The ability of exotic plants to displace natives is often attributed to physiological characteristics such as rapid growth conferring competitive ability. The ability of an exotic to displace natives, however, is a product of physiological traits and the environment. Invasion occurs under conditions that allow traits such as rapid growth to be expressed. We examine differences in N uptake between two native perennial grasses: Elymus elymoides and Pseudoroegneria spicata; two invasive annual grasses; Bromus tectorum and Taeniatherum caput-medusae; and one highly selected non-native perennial grass: Agropyron cristatum at various springtime temperatures. All species are found throughout the Intermountain West, USA. Averaged among temperatures, annual grasses had higher N uptake than native perennials and expressed traits consistent with an acquisitive life history. The strongest predictor of whole-plant N uptake was specific absorption rate (SAR) which was correlated with leaf N. These findings, however, were not consistent among temperatures. At low temperatures, differences in SAR between annual and native perennials were minor and specific root length and root [N] were not significantly different. Energy availability similarily limited N uptake in native and invasive grasses. A model of SAR based on temperature dependence of respiration identified differences among species, but not between invasive and native species. The model suggests B. tectorum, T. caput-medusae, and E. elymoides allocate a constant fraction of total energy harvested SAR while A. cristatum and P. spicata allocate an absolute amount of energy to SAR regardless of energy available. Our findings highlight the context-dependent nature of performance differences between native and invasive plant species.