Background
The authors write that "phytoextraction is the use of plants to remove organic and/or inorganic contaminants from the environment (Lasat, 2002)," and they say that "if both the biomass and heavy metal concentration are increased in the aboveground tissues of plants grown in heavy metal contaminated soils at an elevated CO2 level, the efficiency of phytoextraction will be improved."

So what did they do? ... what did they find?? ... and what does it mean???

What was done
Zheng et al. grew well watered and fertilized three-week-old sun ferns (Pteridium revolutum) derived from rhizome cuttings for 20 additional days in pots containing 1 kg of local topsoil at three concentrations of added soil copper (Cu) contamination in both ambient air and air enriched with an extra 350 ppm of CO2 (from 08:00 to 11:00 of each sunny day of that period), after which they measured the amount of frond biomass produced in each CO2 treatment and the copper concentrations in the fern's fronds.

What was learned
The doubling of the air's CO2 concentration (from 350 to 700 ppm) increased frond biomass production by 36% in the soil to which no copper was added, by 69% in the soil containing an extra 50 mg Cu per kg soil, and by 66% in the soil containing an extra 150 mg Cu per kg soil. It also increased frond copper concentration by 27% in the soil to which no copper was added, by 1% in the soil containing an extra 50 mg Cu per kg soil, and by 26% in the soil containing an extra 150 mg Cu per kg soil. The end result was a 72% increase in the total Cu content of the fronds grown in the soil to which no copper was added, a 70% increase in the Cu content of the fronds grown in the soil to which an extra 50 mg Cu per kg soil was added, and a 107% increase in the Cu content of the fronds grown in the soil to which an extra 150 mg Cu per kg soil was added.

What it means
The five Chinese scientists conclude that P. revolutum could serve as a "good candidate" for the phytoextraction of copper from Cu-contaminated soils, and that "doubling the ambient CO2 concentration will facilitate its use in phytoextraction." Hence, it can be appreciated that the reclamation of copper-contaminated soils by "phytoextractants" will likely proceed at a much faster pace in a high-CO2 world of the future than it does currently, which is good news for man and nature alike, since Paytan et al. (2009) report that "anthropogenic emissions are increasing atmospheric copper deposition sharply," as are copper mining operations in countries such as China.

References
Lasat, M.M. 2002. Phytoextraction of toxic metals: A review of biological mechanisms. Journal of Environmental Quality 31: 109-120.

Paytan, A., Mackey, K.R.M., Chen, Y., Lima, I.D., Doney, S.C., Mahowald, N., Labiosa, R. and Postf, A.F. 2009. Toxicity of atmospheric aerosols on marine phytoplankton. Proceedings of the National Academy of Sciences, USA 106: 10.1073/pnas.0811486106.