What was done
Stem respiration rates of three Populus species -- P. alba L. (Clone 2AS-11), P. nigra L. (Clone Jean Pourtet), and P. x euramericana (Clone I-214) -- were measured in a high-density forest plantation in the third year of a FACE study in which the CO2 concentration of the air surrounding the trees was increased to a target value of 550 ppm.

What was learned
Although the standing woody biomass of the three Populus species was significantly larger after three years of CO2 enrichment compared to the trees exposed to ambient air, the authors report that "stem respiration rates were not affected by the FACE treatment."  In addition, they note that "FACE did not influence the relationships between respiration rate and both stem temperature and relative growth rate."

What it means
Since the authors reported "no effect of the FACE treatment on Rm [maintenance respiration, which is related to the sustaining of existing cells] and Rg [growth respiration, which is related to the synthesis of new tissues]," it would appear that the enhanced fixing of carbon by increased rates of photosynthesis in a CO2-enriched world of the future will indeed translate into enhanced growth rates and sequestering of carbon by the world's woody plants, as was found in this study.