What was done
Circular FACE plots (30-m diameter) receiving 350 and 560 ppm CO2 were established in a 13-year-old loblolly pine (Pinus taeda) plantation in North Carolina, USA, to determine the effects of elevated CO2 on this important timber species.  This paper describes the effects of elevated CO2 on belowground root dynamics, as assessed by minirhizotrons inserted into the low-nutrient (nitrogen and phosphorus) soils of the experimental plots.

What was learned
After one year of treatment, total standing root length and root numbers per minirhizotron were 16 and 34% greater, respectively, in the CO2-enriched plots than in the ambient-air plots.  In addition, elevated CO2 increased the diameter of living and dead roots by 8 and 6%, respectively.  Furthermore, annual root production and root mortality were 26 and 46% greater in the CO2-enriched plots than they were in the control plots.

What it means
As the CO2 content of the air continues to increase, loblolly pine plantations will likely experience increases in belowground biomass production that lead to longer and larger-diameter root systems.  Hence, as the atmospheric CO2 concentration increases, greater amounts of carbon will be allocated belowground by loblolly pine plantations, which will likely result in enhanced carbon sequestration within the soils in which they are rooted.