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Reclaiming Cadmium-Contaminated Soil with Poplars and Willows
Wang, R., Dai, S., Tang, S., Tian, S., Song, Z., Deng, X., Ding, Y., Zou, X., Zhao, Y. and Smith, D.L. 2012. Growth, gas exchange, root morphology and cadmium uptake responses of poplars and willows grown on cadmium-contaminated soil to elevated CO2. Environmental Earth Sciences 67: 1-13.

The authors state that heavy metal pollution in agricultural soils is receiving ever more attention, citing Tang (2006) and the IPCC (2007), while noting that China possesses more than 130 km2 of cadmium (Cd) contaminated soil due to wastewater discharge from mining operations and industrial emissions, citing Xiong et al. (2004) and Yu and Zhou (2009). And knowing of the ability of atmospheric CO2 enrichment to enhance plant growth and increase the amounts of various substances they extract from the soil, they decided to conduct a study of the potential for this phenomenon to serve as a means of phytoremediation of Cd-contaminated soils.

What was done
Working with one poplar genotype [Populus euramericana cv. '74/76' (P107)] and two willow genotypes [Salix jiangsuensis CL. '799' (J799) and Salix jiangsuensis CL. '172' (J172)], Wang et al. measured photosynthesis, plant growth, root morphology and Cd uptake in the three species when they were grown for 40 days under adequate irrigation in pots filled with Cd-contaminated soil that were placed in six open-top chambers supplied with either ambient or elevated CO2 (360 or 800 ppm) from 09:30 to 17:30 hours every day that was not overcast.

What was learned
In the words of the ten researchers, "elevated CO2 increased leaf, root, stem and total biomasses of the three tested tree genotypes, and biomass increase was closely correlated with stimulation of leaf photosynthesis and root growth." In addition, they state that "elevated CO2 increased root lengths, root surface areas, root volumes and numbers of root tips for the three tree genotypes grown on Cd-contaminated soil, and, consequently, enhanced the ability to capture Cd in root systems and led to increased total Cd uptake in all plant parts."

What it means
As the air's CO2 content continues to rise, the employment of phytoremediation of contaminated soil should become ever more effective.

IPCC. 2007. Climate Change 2007: The Physical Science Basis. Solomon, S., Qin, D., Manniing, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L. (Eds.), Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

Tang, S.R. 2006. The Principle and Methods of Phytoremediation of Contaminated Environment. Scientific Press, Beijing, China.

Xiong, X., Allinson, G., Stagnitti, F., Li, P., Wang, X., Liu, W., Allinson, M., Turoczy, N. and Peterson, J. 2004. Cadmium contamination of soils of the Shenyang Zhangshi Irrigation Area, China: an historical perspective. Bulletin of Environmental Contamination and Toxicology 73: 270-275.

Yu, Z.G. and Zhou, Q.X. 2009. Growth responses and cadmium accumulation of Mirabilis jalapa L. under interaction between cadmium and phosphorus. Journal of Hazardous Materials 167: 38-43.

Reviewed 30 January 2013