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Atmospheric CO2 Enrichment Effects on Pharmacological Substances Produced by Plants
Reference
Ziska, L.H., Emche, S.D., Johnson, E.L., George, K., Reed, D.R. and Sicher, R.C.  2005.  Alterations in the production and concentration of selected alkaloids as a function of rising atmospheric carbon dioxide and air temperature: implications for ethno-pharmacology.  Global Change Biology 11: 1798-1807.

What was done
The authors grew well watered and fertilized tobacco (Nicotiana tabacum L.) and jimson weed (Datura stramonium L.) plants from seed (one plant per 0.6-L pot filled with promix for tobacco and vermiculite for jimson weed) in controlled environment chambers maintained at atmospheric CO2 concentrations of either 294, 378 or 690 ppm and mean air temperatures of either 22.1 or 27.1C for 50 and 47 days after planting for tobacco and jimson weed, respectively, while sampling the plants at weekly intervals beginning at 28 and 16 days after planting for tobacco and jimson weed, respectively, to determine the effects of these treatments on the concentrations of three plant alkaloids possessing important pharmacological properties: nicotine, in the case of tobacco, and atropine and scopolamine, in the case of jimson weed.

What was learned
First of all, at the time of the final harvesting of both plant species, the elevated CO2 treatment was found to have increased the aboveground biomass production of tobacco by approximately 89% at 22.1C and 53% at 27.1C, and to have increased that of jimson weed by approximately 23% and 14% at the same respective temperatures.  It was also found to have reduced the concentration of nicotine in tobacco, to have increased the concentration of scopolamine in jimson weed, but to have had no significant effect on the concentration of atropine in jimson weed.

What it means
This study demonstrates that as the air's CO2 content continues to rise, there will likely be significant changes in the health-promoting (or health-harming!) properties of many of the plant-produced substances that people take into their bodies on a daily basis.  In the alkaloids studied by Ziska et al., the observed changes (reduced nicotine in tobacco and increased scopolamine in jimson weed) would likely be characterized as positive; for they report that nicotine is "universally acknowledged as having significant negative impacts on human health (Topliss et al., 2002)," and that scopolamine is used as a sedative and as "an antispasmodic in certain disorders characterized by restlessness and agitation, (e.g., delirium tremens, psychosis, mania and Parkinsonism)."

Other CO2-induced positive changes in plant-produced substances that promote human health are also noted by Ziska et al., including increases in the antidepressants hypercin and pseudohypericin in St Johns wort, the cardiac glycoside digoxin in wooly foxgolove, and several purported anticancer constituents of spider lilies.  These findings, as well as many others, are described in more detail in our Subject Index under the general heading Health Effects (Carbon Dioxide).

With respect to the significance of these findings, Ziska et al. say "it can be argued that synthetic production of these secondary compounds alleviates any concern regarding environmental impacts on their production from botanical sources; however, developing countries (i.e., ~75% of the world population) continue to rely on ethno-botanical remedies as their primary medicine (e.g. use of alkaloids from jimson weed as treatment for asthma among native Americans and in India)," also noting that "for both developed and developing countries, there are a number of economically important pharmaceuticals derived solely from plants whose economic value is considerable (Raskin et al., 2002)."  In addition, we would add that many of these CO2-enhanced health-promoting substances are found in some of the common foods we eat, such as vitamin C in oranges (Idso et al., 2002) and strawberries (Wang et al., 2003), the latter of which fruit also contain a number of other CO2-enhanced antioxidants, as well as numerous CO2-enhanced flavonoids, phenolics and anthocyanins.

References
Idso, S.B., Kimball, B.A., Shaw, P.E., Widmer, W., Vanderslice, J.T., Higgs, D.J., Montanari, A. and Clark, W.D.  2002.  The effect of elevated atmospheric CO2 on the vitamin C concentration of (sour) orange juice.  Agriculture, Ecosystems and Environment 90: 1-7.

Raskin, I., Ribnicky, D.M., Komarnytsky, S. et al.  2002.  Plants and human health in the twenty-first century.  Trends in Biotechnology 20: 522-531.

Topliss, J.G., Clark, A.M., Ernst, E. et al.  2002.  Natural and synthetic substances related to human health.  Pure and Applied Chemistry 74: 1957-1985.

Wang, S.Y., Bunce, J.A. and Maas, J.L.  2003.  Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries.  Journal of Agricultural and Food Chemistry 51: 4315-4320.

Reviewed 28 December 2005