Technical Abstract: Climate change driven by increasing atmospheric CO2 concentrations is causing measurable changes in precipitation patterns. Most climate change scenarios forecast continuing increases in extreme precipitation patterns for North American terrestrial ecosystems, manifest as larger precipitation events separated by longer dry periods, with still uncertain implications for key processes controlling terrestrial ecosystem structure and function. Changes in the size of precipitation events may cause differential responses in the processes controlling the uptake and loss of C, and therefore could alter carbon sequestration in terrestrial ecosystems. Here we show that more extreme precipitation patterns (longer intervals between events combined with larger events) shifted experimental grasslands toward greater net uptake of C, and also made C fluxes less responsive to variation in event size, changes which could lead to increased C-sequestration under more extreme precipitation regimes. These results have important implications for terrestrial ecosystem responses to climate change. More extreme precipitation regimes may reinforce increases in C-sequestration expected to result from increasing atmospheric [CO2], but may also lower plant water status and productivity. Thus, these results highlight the need for improved forecasts of precipitation pattern as well as quantity and field experiments that manipulate CO2, temperature, and precipitation in combination in order to improve forecasts of ecosystem carbon dynamics.