What was done
Monoliths of two contrasting grasslands, a species-rich turf growing over limestone and a species-poor turf growing over a peaty soil, were transferred from Moor House National Nature Reserve in the United Kingdom to four "Solardomes" at Lancaster University, where they were maintained for two years under natural daylight and air temperatures close to ambient.  One set of two solardomes was exposed to ambient air and another identical set to air enriched with an extra 250 ppm CO2.  At various times throughout the experiment, a number of measurements of above- and below-ground growth were made.

What was learned
Shoot biomass was unaltered by the elevated level of atmospheric CO2; but root biomass was enhanced by 40 to 50%.  Furthermore, especially in the peat soil, root turnover was highly accelerated in the CO2-enriched treatment, so much so, in fact, that the authors concluded that the increase in root biomass observed at the end of the experiment "was almost certainly a large underestimate of the amount of carbon transferred to the soil."

What it means
The authors conclude that the increased productivity that the two grassland ecosystems exhibited under elevated atmospheric CO2 concentrations, along with the consequent increases in soil organic matter, are "likely to persist."  Hence, it can be appreciated that the ongoing rise in the air's CO2 content should stimulate these grassland ecosystems to sequester ever more carbon in their soils, thus helping to slow the rate of rise of the atmosphere's CO2 concentration.