Background
In the introduction to their study, Kretzschmar et al. write that "isoflavonoids constitute a group of natural products derived from the phenylpropanoid pathway, which is abundant in soybeans," and that "the inducible accumulation of low molecular weight antimicrobial pterocarpan phytoalexins, the glyceollins, is one of the major defense mechanisms implicated in soybean resistance."

What was done
The authors, as they describe it, "evaluated the effect of an elevated CO2 atmosphere on the production of soybean defensive secondary chemicals induced by nitric oxide and a fungal elicitor." This they did in a glasshouse study where they grew soybeans from seed for a period of nine days in large well-watered pots placed within open-top chambers that were maintained at atmospheric CO2 concentrations of either 380 or 760 ppm, while they examined changes in the production of phytoalexins and some of their precursors in the activity of three enzymes related to their biosynthetic pathways.

What was learned
Kretzschmar et al. report that "elevated CO2 combined with nitric oxide resulted in an increase of intermediates and diverted end products (daidzein - 127%, coumestrol - 93%, genistein - 93%, luteolin - 89% and apigenin - 238%) with a concomitant increase of 1.5-3.0 times in the activity of enzymes related to their biosynthetic routes."

What it means
The four Brazilian researchers say their findings "indicate changes in the pool of defense-related flavonoids in soybeans due to increased carbon availability, which may differentially alter the responsiveness of soybean plants to pathogens in CO2 atmospheric concentrations such as those predicted for future decades." Put more simply, the ongoing rise in the air's CO2 content will likely increase the ability of soybeans to withstand the attacks of various plant diseases in the years and decades to come, helping the world to better meet the challenge of feeding its still-growing population.