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Soybean Pod Yield: Positive CO2 Effect vs. Negative O3 Effect
Booker, F.L. and Fiscus, E.L.  2005.  The role of ozone flux and antioxidants in the suppression of ozone injury by elevated CO2 in soybean.  Journal of Experimental Botany 56: 2139-2151.

What was done
In a two-year experiment, well watered and fertilized soybean (Glycine max (L.) Merr.) plants were grown out-of-doors in pots in open-top chambers from emergence to maturity while exposed to either charcoal-filtered air, or charcoal-filtered air plus an extra 336 ppm CO2, or charcoal-filtered air plus 1.5 times normal ambient O3, or charcoal-filtered air plus an extra 336 ppm CO2 and 1.5 times normal ambient O3.

What was learned
The imposition of elevated CO2 alone increased soybean pod biomass by 23.0%, the imposition of elevated O3 alone decreased pod biomass by 13.3%, while the imposition of elevated CO2 and O3 together increased pod biomass by 23.0%.

What it means
There are two ways of thinking about these results.  If one first considers the negative effect of elevated ozone, adding extra CO2 is seen to more than completely ameliorate ozone's negative effect on pod biomass.  If, on the other hand, one first considers the positive effect of elevated CO2, adding ozone is seen to have absolutely no effect on CO2's positive effect.  Consequently, it can be appreciated that the positive effect of elevated CO2 in this study was vastly superior to the negative effect of elevated ozone.  In fact, it totally dominated.

In commenting on their results, Booker and Fiscus state that, "overall, elevated CO2 concentration counteracted the detrimental effects of O3 on growth and yield," noting that "this response has been observed in previous studies with soybean and other crop species (Unsworth and Hogsett, 1996; Olszyk et al., 2000; Ainsworth et al., 2002; Fiscus et al., 2002, 2005; Morgan et al., 2003; Cardoso-Vilhena et al., 2004; Booker et al., 2005)."

Ainsworth, E.A., Davey, P.A., Bernacchi, C.J., et al.  2002.  A meta-analysis of elevated [CO2] effects on soybean (Glycine max) physiology, growth and yield.  Global Change Biology 8: 695-709.

Booker, F.L., Miller, J.E., Fiscus, E.L., Pursley, W.A. and Stefanski, L.A.  2005.  Comparative responses of container- versus ground-grown soybean to elevated CO2 and O3Crop Science 45: 883-895.

Cardoso-Vilhena, J., Balaguer, L., Eamus, D., Ollerenshaw, J.H. and Barnes, J.  2004.  Mechanisms underlying the amelioration of O3-induced damage by elevated atmospheric concentrations of CO2Journal of Experimental Botany 55: 771-781.

Fiscus, E.L., Booker, F.L. and Burkey, K.O.  2005.  Crop responses to ozone: uptake, modes of action, carbon assimilation and partitioning.  Plant, Cell and Environment 28: 10.1111/j.1365-3040.2005.01349.x.

Fiscus, E.L., Miller, J.E., Booker, F.L., Heagle, A.S. and Reid, C.D.  2002.  The impact of ozone and other limitations on the crop productivity response to CO2Technology 8: 181-192.

Morgan, P.B., Ainsworth, E.A. and Long, S.P.  2003.  How does elevated ozone impact soybean? A meta-analysis of photosynthesis, growth and yield.  Plant, Cell and Environment 26: 1317-1328.

Olszyk, D.M., Tingey, D.T., Watrud, L., Seidler, R. and Andersen, C.  2000.  Interactive effects of O3 and CO2: implications for terrestrial ecosystems. In: Sing, S.N., ed. Trace Gas Emissions and Plants.  Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 97-136.

Unsworth, M.H. and Hogsett, W.E.  1996.  Combined effects of changing CO2, temperature, UV-B radiation and O3 on crop growth.  In: Bazzaz, F. and Sombroek, W., eds. Global Climate Change and Agricultural Production. John Wiley and Sons, Chichester, United Kingdom, pp. 171-197.

Reviewed 26 October 2005