The impact of carbon dioxide fertilization on soil carbon storage below a closed-canopy forest

As a result of CO2 fertilization, trees grown in a closed-canopy forest at an elevated concentration of atmospheric CO2 have sequestered more mineral-bound carbon in soil than trees grown at ambient levels of CO 2. CO2 fertilization occurs when elevated carbon dioxide levels enhance plant growth. Soil cores were taken from the Free-Air Carbon Dioxide-Enrichment (FACE) facility in the Duke forest from 1996 to 2000. After 3.5 years of treatment, the uppermost 35 cm of soil from plots growing at an (ambient +200 ppm) CO2 level increased in carbon content ∼30% more than soil from ambient plots. The ambient plots accumulated ∼2900 kg C/ha/yr, while the elevated plots accumulated ∼3700 kg C/ha/yr. This response of a forest to elevated atmospheric CO2 levels suggests that CO2 fertilization may be increasing soil carbon storage in similar closed-canopy forests and slowing the build-up of atmospheric CO 2.