Impacts of Elevated CO2 on Lead Contaminated Soils

Paper Reviewed
Jia, X., Zhang, C., Zhao, Y., Liu, T. and He, Y. 2018. Three years of exposure to lead and elevated CO2 affects lead accumulation and leaf defenses in Robina pseudoacacia L. seedlings. Journal of Hazardous Materials 349: 215-223.

Multiple studies have examined the impact of atmospheric CO2 enrichment on the growth of plants in soils that are polluted with heavy metals (see Heavy Metal Toxicity in our Subject Index), yet relatively few of them have focused on lead as the metal contaminant. Lead (Pb), however, is a major pollutant in some terrestrial ecosystems. When present in high concentrations, it can significantly reduce seed germination and negatively impact plant growth.

Recognizing the scarcity of such studies, Jia et al. (2018) set out to conduct a 3-year experiment in an effort to determine the response of black locust (Robina pseudoacacia) seedlings to the combined effects of elevated atmospheric CO2 and lead contamination. Their work was conducted in plastic pots in open-top chambers at Chang’an University, Xi’an, China, where atmospheric CO2 concentrations were maintained at either ambient (385 ppm) or elevated (700 ppm) levels and soils were kept at either normal (15.56 mg Pb per kg of dry soil) or contaminated (500 mg Pb per kg of dry soil) lead conditions. And what did their experiment reveal?

In terms of plant growth, Jia et al. report that at the end of their 3-year experiment, seedling height and width were both enhanced by elevated CO2, regardless of Pb treatment. Additionally, elevated CO2 increased the production of “soluble sugars, proline, flavonoids, saponins, and phenolics in plants exposed to Pb stress,” which substances can help to reduce and eliminate reactive oxygen species that can damage plants in response to heavy metal toxicity stress. Jia et al., also report that elevated CO2 “increased Pb accumulation in leaves and Pb removal rate in soils,” thereby enhancing “the phytoextraction of Pb from contaminated soils.” Consequently, elevated CO2 may well help to improve the cleanup of Pb-polluted soils via the natural process of phytoremediation.

This article appeared on the CO2 Science website at http://www.co2science.org/articles/V21/jul/a8.php