What was done
A species-rich nutrient-poor calcareous grassland located in Switzerland was exposed to atmospheric CO2 concentrations of 360 and 600 ppm for approximately six years to study the long-term effects of elevated CO2 on this grassland community.  Bromus erectus Huds., which accounts for approximately half of the aboveground vegetative biomass, dominates this ecosystem.

What was learned
Elevated CO2 increased carbon (C) stocks (g C per m² ground surface area) in plant shoots and roots by 17 and 24%, respectively.  Similarly, atmospheric CO2 enrichment enhanced carbon stocks in vegetative litter by 34%.  The net effect of elevated CO2 on these carbon stocks resulted in an initial rate of carbon flux into the soil of 210 g C m^-2 year^-1.  After six years of treatment, however, CO2-enriched soils only held about 44% of the carbon stocks expected from this influx rate, due to a low soil residence time for this newly-input carbon.  Nonetheless, the data demonstrate that carbon sequestration in low-nutrient soils can in fact be enhanced as a result of atmospheric CO2 enrichment.

What it means
As the atmospheric CO2 concentration rises, nutrient-poor calcareous grasslands will likely display enhanced rates of photosynthesis and biomass production that ultimately lead to greater soil carbon sequestration.