Paper Reviewed
Guo, B., Dai, S., Wang, R., Guo, J., Ding, Y. and Xu, Y. 2015. Environmental and Experimental Botany 115: 1-10.

Introducing their work, Guo et al. (2015) write that the oft-observed high cadmium (Cd) concentrations in agricultural soils "inhibit photosynthesis and growth as well as diminish water and nutrient uptake," citing He et al. (2011), Liu et al. (2011) and Elobeid et al. (2012). In addition, they note that "Cd induces oxidative stress and initiates membrane lipid peroxidation, thereby causing severe damage to membrane systems, cell organelles and DNA," citing Schutzendubel and Polle (2002), Wang et al. (2008), He et al. (2013a,b, and 2015), Jin et al. (2013) and Polle et al. (2013). And, therefore, they describe how they went on to study the combined effects of elevated CO2 (EC) and Cd on one particular poplar genotype (Populus x euramericana (Dode) cv. 'Nanlin-95' (NL95)) and one willow genotype (Salix jiangsuensis CL, '172' (J172)), which they grew in three Cd-contaminated soils (Cd concentrations of either 0, 5 or 25 mg Cd/kg soil) in six open-top chambers maintained continuously at CO2 concentrations of either the normal ambient value of 360 ppm or an enriched value of 800 ppm from 7:00 to 20:00 over the 90-day period from 1 June 2010 to 29 September 2010.

This work revealed, as the six Chinese scientists report, that at EC levels for both species, plant growth, CO2 assimilation rate and intrinsic water use efficiency were increased, while stomatal conductance and transpiration rate were decreased and Cd concentrations were unchanged. In addition, they say that "EC also decreased malondialdehyde content in the two species grown in Cd-contaminated soil and increased antioxidant enzymatic activities in J172 grown in high Cd-contaminated soil," while "at EC, plant growth and total Cd uptake exhibited greater increase in high Cd-contaminated soil than in low Cd-contaminated soil."

As for the significance of these findings, Guo et al. conclude that, taken together, "these findings suggest that EC stimulated plant growth by increasing leaf photosynthesis" and that it "enhanced phytoremediation efficiency, particularly at high levels of Cd exposure." And they further note, in this regard, that under the high Cd treatment, "the well-maintained photosynthesis is assumed responsible for decreasing reactive oxygen species accumulation and avoiding membrane lipid peroxidation."

References
Elobeid, M., Gobel, C., Feussner, I. and Polle, A. 2012. Cadmium interferes with auxin physiology and lignification in poplar. Journal of Experimental Botany 63: 1413-1421.

He, J.L., Qin, J.J., Long, L.Y., Ma, Y.L., Li, H., Li, K., Jiang, X.N., Liu, T.X., Polle, A., Liang, Z.S. and Luo, Z. B. 2011. Net cadmium flux and accumulation reveal tissue-specific oxidative stress and detoxification in Populus x canescens. Physiologia Plantarum 143: 50-63.

He, J.L., Li, H., Luo, J., Ma, C.F., Li, S.J., Qu, L., Gai, Y., Jiang, X.N., Janz, D., Polle, A., Tyree, M. and Luo, Z.B. 2013a. A transcriptomic network underlies microstructural and physiological responses to cadmium in Populus x canescens. Plant Physiology 162: 424-439.

He, J.L., Ma, C.F., Ma, Y.L., Li, H., Kang, J.Q., Liu, T.X., Polle, A., Peng, C.H. and Luo, Z.B. 2013b. Cadmium tolerance in six poplar species. Environmental Science and Pollution Research 20: 163-174.

He, J.L., Li, H., Ma, C.F., Zhang, Y.L., Polle, A., Rennenberg, H., Cheng, X.Q. and Luo, Z.B. 2015. Overexpression of bacterial ?-glutamylcysteine synthetase mediates changes in cadmium influx allocation, and detoxification in poplar. New Phytologist 205: 240-254.

Jin, C.W., Mao, Q.Q., Luo, B.F., Lin, X.Y. and Du, S.T. 2013. Mutation of mpk6 enhances cadmium tolerance in Arabidopsis plants by alleviating oxidative stress. Plant and Soil 371: 387-396.

Liu, C.F., Guo, J.L., Cui, Y.L., Lu, T.F., Zhang, X.H. and Shi, G.R. 2011. Effects of cadmium and salicylic acid on growth, spectral reflectance and photosynthesis of castor bean seedlings. Plant and Soil 344: 131-141.

Polle, A., Klein, T. and Kettner, C. 2013. Impact of cadmium on young plants of Populus euphratica and P. x canescens, two poplar species that differ in stress tolerance. New Forests 44: 13-22.

Schutzendubel, A. and Polle, A. 2002. Plant responses to abiotic stresses: heavy metal induced oxidative stress and protection by mycorrhization. Journal of Experimental Botany 53: 1351-1365.

Wang, Z., Zhang, Y.X., Huang, Z.B. and Huang, L. 2008. Antioxidative response of metal-accumulator and non-accumulator plants under cadmium stress. Plant and Soil 310: 137-149.