What was done
Three-year-old seedlings of beech (Fagus sylvatica L.) were grown for six weeks in controlled environmental chambers receiving atmospheric CO2 concentrations (¹³CO2) of 350 and 700 ppm to study the effects of elevated CO2 on carbon uptake in this important tree species.  In addition, plants were watered with nutrient solutions containing ¹⁵NH4¹⁵NO3 to study the effect of elevated CO2 on nitrogen uptake.  Thus, the authors utilized stable isotopes of carbon and nitrogen to measure their uptake and disposition in this species.

What was learned
Elevated CO2 significantly increased seedling carbon uptake by 63% without altering its allocation among plant organs.  Nitrogen uptake, however, was not affected by elevated CO2, nor was its allocation among plant organs.  Consequently, the leaf carbon-to-nitrogen ratio increased by 26% with atmospheric CO2 enrichment.

What it means
As the air's CO2 content rises, beech seedlings will likely display enhanced rates of carbon uptake that will ultimately lead to increases in biomass.  Indeed, the majority of the carbon taken up by the beech seedlings of this study was allocated to the early development of leaves, which should subsequently support greater absolute amounts of photosynthetic carbon fixation.  Thus, carbon sequestration in beech trees will likely increase with future increases in the air's CO2 content.