Soil Carbon Turnover and Inventories for a Native Forest and Cultivated Site in Indiana

Soil Carbon Turnover and Inventories for a Native Forest and Cultivated Site in Indiana

We have calculated the residence time and inventory for active soil carbon for paired native and cultivated sites in Indiana using total carbon, C-13, and radiocarbon measurements of carbon from soil. We estimate that the active soil carbon inventory is 25 years and that inventories range from 750 to 940 GtC. Active soil carbon exchanges between 30 and 38 Gt C with the atmosphere annually, which about half of the annual net primary productivity. These results suggest that native soil carbon has the potential to respond to CO2 fertilization, climatic change, anthropogenic nitrogen deposition, and changing land use. Hence, soil carbon has the potential to significantly alter atmospheric CO2 levels. The cultivated site had lower radiocarbon values than the native site. We estimate that CO2 levels of 560 ppm (twice pre-industrial levels) may transfer 310 Gt C from the atmosphere to the soil because of CO2 fertilization. In contrast, glacial CO2 levels of 200ppm may have released 460 Gt C from the soil to the atmosphere because of "CO2 starvation".