What was done
The authors rooted eight saplings (of different genotypes) of beech (Fagus sylvatica) and Norway spruce (Picea abies) directly into calcareous or acidic soils in open-top chambers and exposed them to atmospheric CO2 concentrations of 370 or 570 ppm and low or high soil nitrogen contents for one year to determine the initial effects of elevated CO2 and soil quality on their biomass production.

What was learned
Elevated CO2 increased biomass production in beech and spruce saplings in a soil-dependent manner.  Beech saplings exhibited a 9% increase in stem diameter increment when grown on calcareous soils, while spruce saplings exhibited an 11% enhancement, but only when grown on acidic soils.

What it means
As the CO2 content of the air continues to rise, the initial growth responses of beech and spruce saplings will likely be modest and dependent upon the type of soil in which the trees are rooted.  Over time, the authors speculate that these initial "small differences during the early experimental phase may cumulate to higher 'final' tree biomass through compounding interest."