What was done
In the words of the authors, "meta-analytic techniques were used to quantitatively summarize the response of soybean to an average, chronic ozone [O3] exposure of 70 ppb, from 53 peer-reviewed studies," after which the net effect of concurrently elevated O3 and CO2 (to unspecified concentrations described as being "above 400 ppm") was similarly derived.

What was learned
Morgan et al. report that "at maturity, the average shoot biomass was decreased 34% and seed yield was 24% lower" in response to elevated O3 alone.  However, they note that "when both O3 and CO2 are elevated, the mean decrease in photosynthesis is 7%," which "compares to a 20% loss for plants grown at elevated O3 and the current ambient CO2."  Likewise, they report that "seed yield decreases for plants grown in elevated O3 and elevated CO2 are only half of those for plants grown in current ambient CO2 and elevated O3."

The three scientists also note "there were significant ozone responses in several plant parameters at low daily average concentrations (less than 60 ppb)," which is less than current concentrations in many locations.  In fact, they report that in studies where the O3 treatment average was less than 60 ppb, "seed yield, shoot and root dry weight were all significantly decreased by about 10%," which suggests that in these circumstances the degree of atmospheric CO2 enrichment employed in the joint O3/CO2 experiments likely would have completely eradicated the O3-induced losses in plant production.

What it means
Clearly, the ongoing rise in the air's CO2 concentration will be an important factor in helping to maintain, and hopefully improve, the productivity of crops such as soybean in the years and decades ahead, when enhanced productivity on ever more valuable land [see our Editorial of 4 Sep 2002] with dwindling water supplies [see our Editorial of 21 Feb 2001] will be sorely needed to feed the world's growing human population.