Competition for soil resources is a driving force in plant community ecology. Therefore, amendments that alter soil resources should affect vegetation dynamics and are potential tools for controlling exotic species. We tested the effects of two types of carbon addition, sugar and activated carbon (AC), on an exotic-dominated grassland plant community. Sugar stimulates the microbial community and temporarily reduces plant available nitrogen (N), while AC adsorbs plant available N. Six experimental plots and three carbon treatments were used: sugar (1000 g m^-2; 42% C), AC (420 g m^-2; 100% C), and control. Treatments were applied in a split-plot design in spring 2008. Aboveground biomass, plant cover, species richness, and plant basal area were tracked for two growing seasons. Although total biomass was not affected by C addition, the distribution of biomass among life forms was affected: carbon addition reduced forb biomass but had no effect on grasses or legumes. Total cover was lower in sugar-treated plots, and sugar also altered the proportional composition of that cover by reducing the abundance of forbs, especially in the first year. Five species were particularly sensitive to sugar addition: Myosotis discolor, Sonchus asper, Taraxacum officinale, Valerianella locusta, and Vulpia bromoides. Sugar also reduced plant basal area in the first year. These results suggest that sugar and, to a lesser extent, AC could be useful management tools. Sugar could be applied to areas where herbicide use is undesirable, reducing the abundance of exotic forbs and providing a window of opportunity for native species establishment.