Global warming could change plant growth, and there are differences in response among vegetation types. Plant roots are an important part of plant production, but their response to temperature is weak. Using simulated warming with an open-top chamber, we studied the effects of long-term warming on allocations of underground biomass and carbon in a Kobresia humilis meadow and Potentilla fruticosa shrub meadow on the Qinghai-Tibet Plateau. We analyzed vertical distributions of underground biomass, root carbon content, and soil organic carbon content. The results show the following after long-term warming via the open-top chamber: (1) underground biomass of the K. humilis meadow decreased significantly; (2) underground biomass moved to deeper soil layers in both meadows; (3) root carbon contents of underground biomass at 0-30 cm depths did not change significantly in both meadows, but it increased in the alpine K. humilis meadow from 10 to 30 cm and decreased in the P. fruticosa shrub meadow at depths 20-30 cm; (4) soil organic carbon content did not change significantly in the soil layer 0-30 cm, but it increased in the K. humilis meadow and decreased in the P. fruticosa meadow in the 20-30 cm layer. Such differences in resource allocation will impact regional vegetation succession and the carbon cycle under a background of global warming.