What was done
The authors grew birch seedlings (Betula pendula Roth.) for approximately five months in enclosed environmental chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm.  In addition, seedlings were simultaneously exposed to ambient or elevated (ambient plus 3 °C) air temperatures to study the interactive effects of elevated CO2 and temperature on the growth of this common boreal forest species.

What was learned
During the most rapid phase of growth observed in the study, elevated CO2 increased rates of net photosynthesis by 21 and 28% at ambient and elevated air temperatures, respectively.  These increases in photosynthetic carbon uptake led to corresponding biomass increases of 17 and 18%.

What it means
In general, the results of this study support the prediction that boreal forest growth will be enhanced in the future due to rising atmospheric CO2 concentrations and higher air temperatures.  Indeed, it is likely that rising atmospheric CO2 concentrations will stimulate photosynthetic carbon uptake and utilization in this important forest species, regardless of any increases in air temperature that may occur in the future.  Thus, boreal forests will likely increase their carbon sequestering abilities and lock up ever greater amounts of carbon within their woody tissues as the air's CO2 content continues to rise.