What was done
The authors studied the long-term effects of atmospheric CO2 enrichment on oak (Quercus pubescens Willd.) trees growing near CO2-emitting springs in Tuscany, Italy.  At different distances from the CO2 springs, physiological and biochemical measurements were made on trees that had been exposed to atmospheric CO2 concentrations of approximately 370 and 700 ppm for their entire 40- to 50-year life spans.

What was learned
Oak trees exposed to elevated CO2 exhibited net photosynthetic rates that were 36-77% greater than those exhibited by control trees growing at ambient CO2 concentrations.  Moreover, the CO2-enriched trees showed no signs of photosynthetic downregulation.  Indeed, there were no significant differences among CO2-enriched and control trees with respect to rubisco activity, rubisco content, total nitrogen content, chlorophyll content and carotenoid content.

What it means
As the air's CO2 content rises, it is likely that oak trees - and possibly all trees - will exhibit enhanced rates of photosynthesis and greater biomass production, thereby enhancing terrestrial carbon sequestration.  Indeed, the authors conclude that "enhanced leaf photosynthetic rates at the CO2 springs could increase carbon sequestrating and productivity of whole tree canopies."  Moreover, they state that "higher carbon acquisition by Q. pubescens and other species could slow the rise in atmospheric [CO2]."  We agree with them, especially since their work demonstrated that long-term CO2 exposure did not lead to photosynthetic down regulation in these naturally-growing trees.