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Evolutionary Adaptation to Rising Atmospheric CO2 Concentration
Reference
Frenck, G., van der Linden, L., Mikkelsen, T.N., Brix, H. and Jorgensen, R.B. 2013. Response to multi-generational selection under elevated [CO2] in two temperature regimes suggests enhanced carbon assimilation and increased reproductive output in Brassica napus L. Ecology and Evolution 3: 1163-1172.

Background
Citing Jump and Pe˝uelas (2005) in regard to "the response of plants to rapid climate change," the five Danish authors write that "where the plastic response potential of a population cannot fully compensate stressful changes in environmental conditions, only evolutionary adaptation can prevent wide-ranging declines in fitness and counter the increased risk of extinction." Such is the case, as they note, "especially for sessile organisms like plants, where migration likely fails to track the speed and magnitude of environmental change," and it is within this context that they rightly note that "adaptive responses will be of eminent importance."

What was done
Frenck et al. grew Brassica napus L. plants from seed in four different environments varying in atmospheric CO2 concentration (390 and 650 ppm) and day/night air temperature regimes (19/12 and 24/17°C) both individually and in four different combinations within a phytotron facility at the Technical University of Denmark, where four parallel selection lineages - hereafter referred to as replicate selection linages (RSL) - were initiated in each of the four treatments. The first generation of these plants (F0) was grown from original B. napus seeds until maturity, after which descendent populations of each RSL were produced from seeds chosen randomly out of the pooled seed stock of its corresponding ancestor population. Then, the plants produced from those seeds were grown under the same environmental conditions as the parental population of a given RSL until life cycle completion, which continued through four complete cycles.

What was learned
In terms of final above-ground dry weight (AG DW), the Danish researchers determined that "throughout the multi-generational cultivation, the sum of accumulated AG biomass deviated to higher values from F0 to F4 in high CO2 environments compared to the pattern found under ambient CO2." More specifically, they reported that "under high CO2 growing conditions, AG DW increased ~4.8% and 4.1% at concurrently elevated temperatures, respectively, from F0 to F4," which "CO2-specific response between the start (F0) and final offspring generation (F4) of the experiment significantly contrasts the decreasing of 0.7% and 3.4%, respectively, under low CO2 conditions."

What it means
Noting that they "were able to reveal a dimension of plant-environment feedbacks, which is currently insufficiently investigated and described for the response of plants to future CO2 concentrations," Frenck et al. produced the data needed to demonstrate, as they describe it, that "fast genetic adaptation responses can occur within a small number of subsequent generations," as discussed by Barrett and Schluter (2008). And they concluded their paper by correctly declaring that "the results of this study ask for a broader scientific approach and further investigations in order to define the magnitude of plant responses to rapid environmental change in a multi-generational and evolutionary context."

References
Barrett, R.D.H. and Schluter, D. 2008. Adaptation from standing genetic variation. Trends in Ecology and Evolution 23: 38-44.

Jump, A.S. and Pe˝uelas, J. 2005. Running to stand still: adaptation and the response of plants to rapid climate change. Ecology Letters 8: 1010-1020.

Reviewed 11 September 2013