In species rich grasslands, management factors may affect carbon storage both directly (e.g. defoliation) and indirectly, by altering plant community structure. We set up a mesocosm experiment to separate these direct and indirect effects. Monoliths were sampled from two plots of a semi-natural, species-rich pasture at Theix (France), which had been subjected to contrasted disturbance levels, high versus low grazing, for 14 years. These monoliths were placed in transparent enclosures in natural light and temperature conditions. At the start of the experiment, half of the monoliths in each disturbance treatment were shifted to the opposite disturbance regime. Above and below ground CO2 fluxes were then measured continuously over 2 years. The net below ground carbon storage was positively correlated (P < 0.001) with net ecosystem productivity (NEP) and was negatively correlated (P < 0.001) with above ground net primary productivity. The net canopy photosynthesis, net ecosystem productivity and net below ground carbon storage were significantly higher for ecosystems previously adapted to a low rather than a high disturbance regime, irrespective of the disturbance level during the mesocosm experiment. In contrast, above ground net primary productivity (ANPP) was significantly enhanced by a high disturbance level during the experiment. ANPP and NEP showed a faster response to an increase rather than a decrease in disturbance level during the experiment. Grassland ecosystems adapted to frequent disturbance by,,razing and cutting stored less carbon compared to ecosystems adapted to a low disturbance regime.