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Heavy-Metal (Copper) Contamination of Rice
Jia, H.X., Guo, H.Y., Yin, Y., Wang, Q., Sun, Q., Wang, X.R. and Zhu, J.G. 2007. Responses of rice growth to copper stress under free-air CO2 enrichment (FACE). Chinese Science Bulletin 52: 2636-2641.

The authors write that copper (Cu) is "an essential micronutrient [that] plays a vital role in maintaining normal metabolism in higher plants," but that it "is toxic to plant cells at higher concentrations and causes the inhibition of plant growth or even death."

What was done
Working at the China FACE site near Jiangdu City, Jiangsu Province, Jia et al. grew a Japonica rice cultivar (Wu Xiang Jing 14) in control and Cu-contaminated soil (23.3 vs. 125 mg Cu per kg soil) for one full season at ambient and elevated atmospheric CO2 concentrations (370 vs. 570 ppm), while measuring leaf Cu concentrations at the tillering, jointing, heading and ripening stages of the crop.

What was learned
At the tillering stage of the plants' progression, leaf Cu concentrations in the plants growing in the Cu-contaminated soil of both CO2 treatments were about 90% greater than those in the plants growing in the uncontaminated soil of both CO2 treatments. By the time the plants had reached the jointing stage, however, the mean leaf Cu concentration in the plants growing in the Cu-contaminated soil in the CO2-enriched air had dropped all the way down to the same level as that of the plants growing in uncontaminated soil in ambient air; and this equivalency was maintained throughout the plants' subsequent heading and ripening stages. For the plants growing in contaminated soil in ambient air, however, leaf Cu concentrations were still 50% greater than those of the plants growing in contaminated soil in CO2-enriched air at the end of the experiment.

This study revealed that the negative effect of a more-than-five-fold increase in soil Cu concentration, which increased leaf Cu concentration by approximately 90% at the crop tillering stage, was completely ameliorated throughout the rest of the crop's development by a mere 54% increase in the atmosphere's CO2 concentration.

What it means
The results of this study bode well indeed for the ability of plants in a CO2-enriched world of the future to better deal with the problem of heavy metal soil toxicity; but much more work must be conducted in this poorly-studied area to determine the degree of applicability of this singular study of rice.

Reviewed 20 February 2008