What was done
The authors grew one-year-old heather plants (Calluna vulgaris L.) for two months in greenhouses maintained at atmospheric CO2 concentrations of 380 and 580 ppm in combination with low and high levels of soil nitrogen before exposing them to ¹⁴CO2 for one day to study the fate of recently-fixed carbon in their experimental plant-soil system.

What was learned
Atmospheric CO2 enrichment increased net ¹⁴C uptake in heather by approximately 43%, irrespective of soil nitrogen content.  In addition, soil ¹⁴C increased in elevated CO2 plots by 17 and 25% at low and high soil nitrogen levels, respectively.  Moreover, although total soil respiration was initially higher in CO2-enriched plots (for two days post ¹⁴CO2 labeling), it declined to become significantly lower than the soil respiration rate displayed by plots exposed to ambient air within two weeks; and that trend persisted throughout the remaining four weeks of the study.

What it means
As the CO2 concentration of the air continues to rise, heather plants will probably exhibit increased carbon uptake that will likely result in greater biomass production and greater carbon stores within their associated soils.  Indeed, the authors conclude that "continuous inputs of more recalcitrant structural root material at elevated CO2 may cause the soil to become a sink for C."  Thus, soil carbon sequestration beneath heather communities will likely increase in the future with further increases in the air's CO2 concentration.