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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.
Citing Jump and Peñuelas (2005) in regard to "the response of plants to rapid climate change," the five Danish authors of Frenck et al. (2013) 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."

Against this backdrop, Frenck et al. grew oilseed rape (Brassica napus L.) plants from seed in four different environments varying in atmospheric CO2 concentrations of 390 ppm (ambient) and 650 ppm (enriched) and day/night air temperature regimes of 19/12°C (ambient) and 24/177deg;C (elevated), 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.

At the end of the first generation (F0), elevated CO2 increased the final above-ground dry weight (AG DW) of B. napus in the normal, or ambient, temperature environment by 22%, while in the elevated temperature environment it boosted it by 14%. However, the Danish researchers report 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" (see Figure 1). In other words, with each successive generation, from F0 to F4, the B. napus AG DW plant growth response to elevated CO2 content increased, such that the later generations experienced greater increases than the earlier generations under the same growing conditions. Thus, the CO2-induced 22 and 14% AG DW increases experienced at generation F0 under the ambient and elevated temperature regimes, respectively, were magnified to 27 and18%, respectively, by the end of the experiment at generation F4.


Figure 1. Mean values (± standard error) of aboveground dry weight at final harvest determined for the four replicate selection linages of Brassica napus grown in the Frenck et al. study. F0 = the ancestral stock population, F4 = the fourth descendant population. Environmental treatments were as follows: green = ambient temperature and ambient CO2 (control), blue = ambient temperature and elevated CO2, red = elevated temperature and ambient CO2, orange = elevated temperature and elevated CO2.

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). This has important implications for all CO2 enrichment studies, as the question remains as to whether or not this generational adaptive capacity exists in other plants. If it does, and if it behaves in similar manner, it could mean that the plant growth benefits of CO2 enrichment are actually greater than what they have long been assumed! Perhaps thinking in this light, Frenck et al. conclude their paper by stating 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."

Additional 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 Peñuelas, J. 2005. Running to stand still: adaptation and the response of plants to rapid climate change. Ecology Letters 8: 1010-1020.

Archived 17 September 2013