Belowground root system is an important part of the prairie ecosystem. Its biomass and net primary productivity have both direct and indirect effects on belowground carbon pool; therefore understanding the seasonal dynamic and turnover of belowground biomass is essential for further understanding of the dynamics, rate and potential of carbon sequestration in grassland ecosystems. Using soil coring method, we studied the dynamics of belowground biomass in relation to temperature and precipitation in meadow steppe and typical steppe grasslands under different land use and management regimes. For the studied grasslands, seasonal dynamic patterns of the aboveground biomass were characterized by unimodal curves. The aboveground biomass was significantly and positively correlated with the previous monthly precipitation (P < 0.05). The seasonal patterns of belowground biomass were characterized by "S" shaped curves in the meadow steppe grasslands, and bimodal curves in the typical steppe grasslands. There were no significant correlations between belowground biomass and temperature or precipitation in either meadow steppe or typical steppe (P > 0.05). Root to shoot ratio decreased throughout the growing season in both meadow steppe and typical steppe grasslands. The vertical distribution of belowground biomass can best be described as exponential curves. Belowground biomass was concentrated at the depth of 0-5 cm in the grasslands dominated by rhizomatous grasses and at 5-10 cm in grasslands dominated by bunch grasses. Belowground net primary productivity ranged from 2167 to 2953 g m^-2 a^-1 in the meadow steppe grasslands; whereas it ranged from 2342 to 3333 g m^-2 a^-1 in the typical steppe grasslands. Carbon storage ranged from 975 to 1329 g m^-2 a^-1 in the meadow steppe grasslands and 1054 to 1450 g m^-2 a^-1 in the typical steppe grasslands. Belowground net primary productivity and carbon storage were 10 times greater than those of aboveground, therefore the belowground system had a larger annual carbon sequestration capacity and was relatively stable. Moreover, net primary productivity was significantly and negatively correlated between above- and belowground (P < 0.05). We conclude that moderate grazing can increase the belowground productivity and carbon storage, however, the long-term overgrazing would significantly reduce the belowground biomass and productivity, and modify their vertical distributions. Belowground biomass and productivity tended to be higher at the upper layer of soil.