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Effects of CO2 and Ozone on Volatile Organic Compounds Emitted by Transgenic and Non-Transgenic Oilseed Rape
Himanen, S.J., Nerg, A.-M., Nissinen, A., Pinto, D.M., Stewart Jr., C.N., Poppy, G.M. and Holopainen, J.K. 2009. Effects of elevated carbon dioxide and ozone on volatile terpenoid emissions and multitrophic communication of transgenic insecticidal oilseed rape (Brassica napus). New Phytologist 181: 174-186.

Plants re-emit a substantial portion of their assimilated CO2 back to the atmosphere as volatile organic compounds (VOCs). These substances affect both the chemical and physical properties of the air, where they generate large quantities of organic aerosols that can impact the planet's climate by forming cloud condensation nuclei that may lead to enhanced cooling during the day by reflecting a greater portion of the incoming solar radiation back to space. In addition, many VOCs protect numerous plants from a host of insect pests.

What was done
To see how these phenomena may be impacted by the ongoing rise in the atmosphere's CO2 concentration, as well as by localized areas and time periods of high ozone (O3) pollution, the authors exposed groups of both normal (non-transgenic) oilseed rape (Brassica napus ssp. oleifera L.) plants and transgenic plants, containing an introduced gene that produces Bacillus thuringiensis (Bt) crystal endotoxin (Cry) proteins that limit herbivorous insect attacks, to air of 360 and 720 ppm CO2, as well as O3-free air and air of 100 ppb O3. These experiments were conducted in controlled-environment chambers, where the plants were grown from seed for 17-18 days in 0.66-liter pots filled with a 2:1:1 mixture of fertilized compost, Sphagnum peat and sand.

What was learned
The non-transgenic plants grown in CO2-enriched air produced 27% more shoot biomass than those grown in ambient air, while the transgenic plants produced 25% more. In the O3-enriched air, on the other hand, the non-transgenic plants produced 29% less shoot biomass than those grown in O3-free air, while the transgenic plants produced 34% less. In addition, on a per-dry-weight basis, Himanen et al. say the "doubled CO2 significantly increased terpenoid emissions from intact oilseed rape plants compared with those released from the corresponding plants grown in control CO2," while they report no O3-induced increases in VOC emissions.

What it means
In addition to the fact that "production of Bacillus thuringiensis crystal endotoxin proteins in a crop plant limits specific herbivorous insect attack without the need for chemical treatments," to quote the seven scientists, "elevated CO2 conditions could modify herbivore-induced defenses [VOC emissions] at the vegetative stage, and enhance indirect defense in the future." And, of course, the increasing CO2 content of the air would help to thwart the growth-reducing effects of ozone pollution at one and the same time.

Reviewed 11 February 2009