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The Impact of Ozone Pollution on Soybean Yields
Morgan, P.B., Mies, T.A., Bollero, G.A., Nelson, R.L. and Long, S.P. 2006. Season-long elevation of ozone concentration to projected 2050 levels under fully open-air conditions substantially decreases the growth and production of soybean. New Phytologist 170: 333-343.

What was done
In the first FACE treatment of a food crop with elevated ozone (O3) concentrations, which was conducted at the SoyFACE facility of the University of Illinois at Urbana-Champaign, USA, the authors exposed an indeterminate soybean (Glycine max L.) cultivar to 1.23 times ambient O3 concentrations during the daylight hours of the 2002 and 2003 growing seasons from 20 days after planting until harvest.

What was learned
The 23% increase in ozone concentration from an average daytime ambient value of 56 ppb to a treatment value of 69 ppb decreased seed yield by an average of 20% (15% in 2002; 25% in 2003). The greater relative yield loss in 2003, according to Morgan et al., "likely resulted from a hailstorm in July that severely damaged the crop," and from the deleterious effects of which the O3-fumigated crop had more trouble recovering, in support of which claim they produce convincing documentation. The researchers also note that the yield losses of both years were significantly larger than what would have been expected (8%) based on the results of more than 30 prior chamber studies of season-long O3 fumigation of soybeans (Ashmore, 2002).

What it means
The elevated O3 concentrations employed in this study were chosen to represent the projected mean increase in tropospheric O3 for 2050 (Prather et al., 2001); but in a commentary on Morgan et al.'s study, Ashmore et al. (2006) state that "the predictions of Dentener et al. (2005) indicate that this increase in ozone concentration could be reached as soon as 2020 in south Asia." Hence, it would appear that large ozone-induced yield losses in soybean (and other crops) are not that far distant in time. As a result, and in light of what we know about the ability of increases in atmospheric CO2 concentration to counter (and often totally compensate for) the deleterious effects of ozone pollution (see Ozone (Effects on Plants) in our Subject Index), we should be thankful that the air's CO2 content is also in an ascending mode.

Ashmore, M.R. 2002. Effects of oxidants at the whole plant and community level. In: Bell, J.N.B. and Treshow, M., Eds. Air Pollution and Plants. J. Wiley, London, UK, pp. 89-118.

Ashmore, M., Toet, S. and Emberson, L. 2006. Ozone - a significant threat to future world food production? New Phytologist 170: 201-204.

Dentener, F., Stevenson, D., Cofala, J., Mechler, R., Amann, M., Bergamaschi, P., Raes, F. and Derwent, R. 2005. The impact of air pollutants and methane emission controls on tropospheric ozone and radiative forcing: CTM calculations for the period 1990-2030. Atmospheric Chemistry and Physics 5: 1731-1755.

Prather, M., Ehhalt, D., Dentener, F., Derwent, R., Dlugokencky, E., Holland, E., Isaksen, I., Katima, J., Kirchhoff, V., Matson, P., Midgley, P. and Wang, M. 2001. Atmospheric chemistry and greenhouse gases. In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linder, P.J., Dai, X., Maskell, K. and Jouhnson, C.A., Eds. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, UK/New York, NY, USA., pp. 239-287.

Reviewed 5 July 2006