Projected changes of carbon balance in mesic grassland ecosystems in response to warming and elevated CO2 using CMIP5 GCM results in the Central Great Plains, USA

Atmospheric CO2 increased in the 20th century and is expected to continue to do so in the 21st century, with resultant warming. Even so, the effects of these changes on the ecological systems, such as carbon sequestration in grassland ecosystems, are still poorly understood. To improve our understanding of the carbon balance, we developed a two-layer soil hydrology model for Terrestrial Ecosystem Model-Hydro Daily to simulate the carbon fluxes of moist grasslands more accurately. Using the outputs of two Representative Concentration Projection scenarios (RCP4.5 and 8.5) from five Coupled Model Inter-comparison Project Phase 5 climate models, we investigated if projected warming and rising atmospheric CO2 could stimulate net primary production (NPP), net ecosystem productivity (NEP), and ecosystem respiration of two highly productive grassland sites in the central Great Plains (USA) in the 21st century. Our study shows that elevated atmospheric CO2 has a fertilization effect in boosting NPP in grassland ecosystems, with a sensitivity of 0.53 gC m−2 yr−1 and 1.06 gC m−2 yr−1 under the RCP4.5 and RCP8.5 climate scenarios, respectively. Warming is more harmful to NPP in the grassland adapted to a warmer climate. Under the RCP4.5 scenario, both grassland sites likely experience a variable net ecosystem carbon exchange. However, the RCP8.5 scenario and accompanying severe warming would turn both grassland sites to net carbon sources by the end of the century, decreasing NEP by 0.97 gC m−2 yr−1 at the warmer site and by 0.96 gC m−2 yr−1 at the cooler site, driven by increased respiration and limited plant growth.