Using a FACE Experiment to Measure the Amount of Carbon Transferred from the Atmosphere to the Soil Because of CO2 Fertilization

R. J. Heumann
Boston College, Dept. of Geology and Geophysics, Chestnut Hill, MA

As a result of CO₂ fertilization, trees grown in a closed-canopy forest at an elevated concentration of atmospheric carbon dioxide have sequestered more mineral-bound carbon in soil than trees grown at ambient levels of carbon dioxide. 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 carbon at a rate of –2900 kg C/ha/yr, while the elevated plots accumulated carbon at a rate of –3700 kg C/ha/yr. Nitrogen inventories also rose substantially more in elevated plots. Ambient plots accumulated nitrogen at a rate of –90 kg N/ha/yr, and elevated plots accumulated nitrogen at a rate of –200 kg N/ha/yr. This may be due to increased nitrogen fixation occurring in the soil because of the increase in available organic carbon. In time, increased N availability may enhance the CO₂ fertilization effect. This response of a forest to elevated atmospheric carbon dioxide levels suggests that CO₂ fertilization may be increasing soil carbon storage in similar closed-canopy forests and slowing the buildup of atmospheric carbon dioxide.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid