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CO2 Effects on Biogenic Volatile Organic Compound Releases from Onions
Jasoni, R., Kane, C., Green, C., Peffley, E., Tissue, D., Thompson, L., Payton, P. and Pare, P.W.  2003.  Altered leaf and root emissions from onion (Allium cepa L.) grown under elevated CO2 conditions.  Environmental and Experimental Botany 51: 273-280.

Pe˝uelas et al. (1995) note that "plants re-emit a substantial fraction of their assimilated carbon into the atmosphere as biogenic volatile organic compounds (BVOCs) that affect the chemical and physical properties of the atmosphere."  Specifically, they say that "BVOCs generate large quantities of organic aerosols (Kavouras et al., 1998) that could affect climate significantly by forming cloud condensation nuclei."  See also, in this regard, Clouds (Condensation Nuclei) and Aerosols (Biological - Terrestrial) in our Subject Index.  "As a result," they continue, "there should be a net cooling of the Earth's surface during the day because of radiation interception."  In addition, Jasoni et al. report that two of the specific odd-chain ketones (2-undecanone and 2-tridecanone) they measure in their study "confer insect resistance against a major agricultural pest, spider mites (Fery and Kennedy, 1987; Chatzivasileiadis and Sabelis, 1997; Chatzivasileiadis et al., 1999)."  Hence, there are a variety of benefits that could result from CO2-induced increases in BVOC emissions.

What was done
The authors grew onion (Allium cepa cv. Purplette) from seed for 30 days in individual cylindrical flow-through growth chambers under controlled environmental conditions at atmospheric CO2 concentrations of either 400 or 1000 ppm.

What was learned
At the end of the study, the plants grown in the CO2-enriched air had an average of 40% more biomass than the plants grown in ambient air, and their photosynthetic rates were 22% greater.  In addition, the CO2-enriched plants exhibited 17-fold and 38-fold increases in emissions of the BVOC hydrocarbons 2-undecanone and 2-tridecanone, respectively.

What it means
Jasoni et al. conclude that their data support the theory that "plants grown under elevated CO2 will accumulate excess carbon and that at least a portion of this excess carbon is funneled into an increased production of BVOCs," which, we might add, have huge positive implications in the realms of both biology and climate, as noted in the Background material of this Journal Review.

Chatzivasileiadis, E.A. and Sabelis, M.W.  1997.  Toxicity of methyl ketones from tomato trichomes to Tetranychu urticea Koch.  Experimental and Applied Acarology 21: 473-484.

Chatzivasileiadis, E.A., Boon, J.J. and Sabelis, M.W.  1999.  Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes.  Experimental and Applied Acarology 23: 1011-1021.

Fery, R.L. and Kennedy, G.G.  1987.  Genetic analysis of 2-tridecanone concentration, leaf tricome characteristics, and tobacco hornworm resistance in tomato.  Journal of the American Society of Horticultural Science 11: 886-891.

Kavouras, I.G., Mihalopoulos, N. and Stephanou, E.G.  1998.  Formation of atmospheric particles from organic acids produced by forests.  Nature 395: 683-686.

Pe˝uelas, J., Llusia, J. and Estiarte, M.  1995.  Terpenoids: a plant language.  Trends in Ecology and Evolution 10: 289.

Reviewed 5 January 2005