Direct and indirect effects of experimental warming on ecosystem carbon processes in a tallgrass prairie

This study was conducted to examine direct and indirect impacts of global warming on carbon processes in a tallgrass prairie in the U.S. Great Plains. Infrared radiators were used to simulate global warming, and clipping was used to mimic hay mowing. Experimental warming caused significant increases in green biomass in spring and autumn and total biomass in summer on most of the measuring dates. Green aboveground biomass showed positive linear correlations with soil temperature in spring and autumn whereas total aboveground biomass in summer was negatively correlated with soil temperature. Experimental warming also affected aboveground biomass indirectly by extending the length of growing season and changing soil nitrogen process. Elevated temperature tended to increase net nitrogen mineralization in the first year but decrease it in the second year, which could be attributable to stimulated plant growth and belowground carbon allocation and consequently enhanced microbial nitrogen immobilization. Warming-induced changes in soil respiration were proportional to those of total aboveground biomass. Clipping significantly reduced aboveground biomass and increased root biomass, but had no effect on net nitrogen mineralization and annual mean soil respiration. The proportional changes in soil respiration to those of aboveground biomass indicate warming-stimulated ecosystem carbon uptake could be weakened by increased carbon release through soil respiration.