Atmospheric carbon dioxide concentrations have increased dramatically since the start of the industrial revolution, and anthropogenic emissions of CO2 continue to increase. The Duke Free Air CO2 Enrichment (FACE) study was initiated in 1996 to test the hypothesis that ecosystems may mitigate anthropogenic CO2 emissions by sequestering extra carbon. Net Primary Production (NPP) has consistently been stimulated by ~20-30% under elevated CO2 at this site, but this has only lead to modest increases in carbon storage in aboveground wood and on the forest floor. There has been no detectable increase in mineral soil carbon under elevated CO2. This study attempts to synthesize 10 years of measurements on belowground carbon cycle processes in an attempt to understand why a consistent stimulation of NPP has not lead to mineral soil carbon storage.
Results of this synthesis suggest that the entire carbon cycle has been sped up by elevated CO2, and that soil organic carbon has been mineralized at an increased rate under elevated CO2 as the trees allocate more carbon belowground to scavenge soil nitrogen. At this point, the trees have been able to find enough soil nitrogen to continue to grow at accelerated rates in elevated CO2, but it is not clear how long this can continue.