Specific leaf area was measured for three dominant perennial grass species in a long term nitrogen fertilization experiment in an abandoned field in Minnesota. The specific leaf area differed among the species and increased with increasing levels of nitrogen fertilization. This increase in specific leaf area was up to 82% for Agropyron repens and shows that the response of specific leaf area to nitrogen fertilization can be highly plastic. Increasing specific leaf area within species, together with a species replacement, resulted in a 202% increase in leaf area index along the nitrogen gradient, whereas the biomass increased by only 57%. One-third of this increase was attributed to species replacement and two-thirds to the change in specific leaf area within species. This plastic response of specific leaf area within plant species substantially increases the aboveground competition for light along nitrogen gradients.