What was done
Open-top chambers were constructed around 13-year-old loblolly pine (Pinus taeda) trees growing on an infertile sandy soil.  The chambers were fumigated for two years with air containing atmospheric CO2 concentrations of either 350 or 550 ppm, while half of the trees at each CO2 concentration received supplemental soil fertilization.

What was learned
Elevated CO2 increased branch needle area by 13%, while soil fertilization increased it by 38%.  Applied together, the effects of the two treatments were additive, enhancing branch needle area by 56%.  In addition, elevated CO2 enhanced the trees' net photosynthesis rates by 82%, with the trees showing no signs of photosynthetic acclimation over the two-year duration of the study.

What it means
As the air's CO2 concentration continues to rise, mature loblolly pine trees will likely respond in a positive manner by exhibiting enhanced rates of photosynthesis and biomass production, regardless of soil nutrition.  Hence, carbon sequestration by mature loblolly pines should proceed at an accelerating pace as well.