What was done
Scots pine (Pinus sylvestris) were grown for three years in open-top chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, during the final two years of this experiment, half of the trees were subjected to a high rate of nutrient supply, while the other half were subjected to a low rate of soil nutrient supply.  Thus, the authors studied the interactive effects of long-term atmospheric CO2 enrichment and nutrient supply on needle physical and chemical properties in this common coniferous tree species.

What was learned
Elevated CO2 increased average needle dry weight by 22 and 72% under low and high nutrient regimes, respectively.  However, atmospheric CO2 enrichment had little or no effects on needle concentrations of terpenes and tannins, which are secondary products of carbon metabolism that affect needle digestibility.  Thus, it is unlikely that rising levels of atmospheric CO2 will impact ecological interactions between this species and the herbivores and decomposers that rely upon its needles for sustenance.

What it means
As the atmospheric CO2 concentration rises, it is likely that Scots pine will exhibit increases in growth and biomass, including the production of larger and heavier needles that have no alterations in their concentrations of carbon based secondary compounds.  Thus, processes that are influenced by these compounds, like decomposition and herbivore food selection, are unlikely to change as the air's CO2 content rises higher and higher.