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The Combined Effects of CO2, Temperature and Drought on Wheat

Paper Reviewed
Dias de Oliveira, E.A., Siddique, K.H.M., Bramley, H., Stefanova, K. and Palta, J.A. 2015. Response of wheat restricted-tillering and vigorous growth traits to variables of climate change. Global Change Biology 21: 857-873.

In setting the stage for their study, Dias de Oliveira et al. (2015) write that "elevated CO2 and high temperature are climate change drivers that, when combined are likely to have an interactive effect on biomass and grain yield," leading to three possible outcomes: (1) a "reduced positive effect of elevated CO2," (2) an "amelioration of the effect of high temperature, or (3) a "synergistic effect where high temperature increases the positive effect of elevated CO2." They also note that the resultant response "may be influenced by [plant] genotypic differences." And in an effort to study such interactions and possibilities, the team of five Australian researchers designed a field experiment to determine the interactive effects of CO2 and temperature, as well as those of a third variable, drought, on two pairs of sister lines of wheat (Triticum aestivum L.) over the course of a growing season, where one of the contrasting pairs of wheat sister lines differed in tillering (free vs reduced), while the other differed in early vigor (high vs low). The experiment was conducted out-of-doors in Western Australia in poly-tunnels under all possible combinations of CO2 concentration (400 or 700 ppm), temperature (ambient or +3°C above ambient daytime temperature), and water status (well-watered or terminal drought post anthesis). So what did the study reveal?

After presenting a very long list of findings, Dias de Oliveira et al. summarized their results as follows: (1) elevated CO2 "increased grain yield and aboveground biomass" (2) terminal drought "reduced grain yield and aboveground biomass," but elevated CO2 "was the key driver in the amelioration of [its negative] effects," (3) "temperature did not have a major effect on ameliorating the effects of terminal drought," and (4) although "the mechanisms by which [the CO2-induced] enhancements were brought about differed in each pair of sister lines," there was "no difference in aboveground biomass or grain yield within each pair." Thus, it would appear that the overall outcome the researchers observed in this study was one in which elevated CO2, acting alone, overpowered the negative effects of a debilitating environmental stress (drought). Consequently, as the air's CO2 concentration rises in the years and decades to come, the negative impacts of drought on wheat biomass and grain yield should diminish. And that is good news worth celebrating!

Posted 4 December 2015