Mineralization of Carbon Stored In the Soil of Forests After Exposure to Elevated Concentrations of Atmospheric Carbon Dioxide and Ozone.

Large scale Free Air Carbon Enrichment experiments have shown that generally there is a substantial increase in forest tree productivity when trees are exposed to elevated atmospheric CO₂. It is often assumed that this increase in productivity will result in increased C storage in the soil, thus partially mitigating the rise in atmospheric CO₂. We measured C mineralization rates in soils taken from forest plots exposed to either: ambient conditions, elevated CO₂, elevated ozone, or elevated CO₂ plus ozone for 12 years. Soils were incubated for one year and the rate of C mineralization was measured. C isotope ratios were also measured in the respired CO₂ to detect the fate of the added CO₂ used during fumigation. The percentage of soil C mineralized during the incubation was significantly greater in soils from CO2 enriched plots, but it was not enough to account for the fate of the increased production in CO₂ enriched plots. The percentage of soil C mineralized was also significantly greater in soils from CO2 and Ozone enriched plots. However, a substantial amount of C originating from the CO₂ enrichment remained in the refractory fraction of soil C.