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 to establish model ecosystems of these forest species and exposed them to atmospheric CO2 concentrations of 370 or 570 ppm and low or high soil nitrogen contents for three years to determine the effects of elevated CO2, nitrogen availability, and soil type on ecosystem gas exchange and tree growth.

What was learned
Elevated CO2 stimulated daytime net ecosystem carbon exchange rates by 58%, regardless of soil type, but had no effect on ecosystem evapotranspiration rates.  Overall, elevated CO2 increased stem dry mass by about 13%, with a slightly greater increase on calcareous as opposed to acidic soils.

What it means
As the CO2 content of the air increases, beech and spruce forests will likely exhibit enhanced carbon exchange rates that should ultimately increase wood production.  In addition, because elevated CO2 had little effect on evapotranspiration, the water-use efficiency of beech and spruce forests should also increase, perhaps allowing such forests to expand their ranges into drier areas.