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/Conclusions

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.